0001384101-19-000010 | 10-K | XBRL Viewer

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Feb. 21, 2019	Jun. 30, 2018
Document and Entity Information
Entity Registrant Name	VERACYTE, INC.
Entity Central Index Key	0001384101
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Public Float			$ 291.6
Entity Common Stock, Shares Outstanding		41,108,741
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 77,995	$ 33,891
Accounts receivable	13,168	12,716
Supplies	3,402	5,324
Prepaid expenses and other current assets	2,387	1,997
Total current assets	96,952	53,928
Property and equipment, net	8,940	9,688
Finite-lived intangible assets, net	12,000	13,067
Goodwill	1,057	1,057
Restricted cash	603	603
Other assets	1,086	326
Total assets	120,638	78,669
Current liabilities:
Accounts payable	2,516	3,853
Accrued liabilities	9,186	8,175
Current portion of long-term debt	1,357	0
Total current liabilities	13,059	12,028
Long-term debt	23,925	24,938
Capital lease liability, net of current portion	0	308
Deferred rent, net of current portion	3,899	4,170
Total liabilities	40,883	41,444
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized, no shares issued and outstanding as of December 31, 2018 and 2017	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized, 40,863,202 and 34,210,388 shares issued and outstanding as of December 31, 2018 and 2017, respectively	41	34
Additional paid-in capital	313,800	248,278
Accumulated deficit	(234,086)	(211,087)
Total stockholders' equity	79,755	37,225
Total liabilities and stockholders' equity	$ 120,638	$ 78,669

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares issued	34,210,388	33,762,278
Common stock, shares outstanding	34,210,388	33,762,278

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 92,008	$ 71,953	$ 65,085
Operating Expenses:
Cost of revenue	33,078	28,195	25,462
Research and development	14,820	13,881	15,324
Selling and marketing	41,313	32,260	28,248
General and administrative	23,963	23,088	23,787
Intangible asset amortization	1,067	1,067	1,067
Total operating expenses	114,241	98,491	93,888
Loss from operations	(22,233)	(26,538)	(28,803)
Interest expense	(1,963)	(4,941)	(2,757)
Other income, net	1,197	476	202
Net loss	(22,999)	(31,003)	(31,358)
Comprehensive loss	$ (22,999)	$ (31,003)	$ (31,358)
Net loss per common share, basic and diluted (in dollars per share)	$ (0.62)	$ (0.91)	$ (1.09)
Shares use to compute net loss per common share, basic and diluted (in shares)	37,020,246	33,925,617	28,830,472

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2015	$ 51,252	$ 28	$ 199,950	$ (148,726)
Balance (in shares) at Dec. 31, 2015		27,685,291
Increase (Decrease) in Stockholders' Equity [Rollforward]
Issuance of common stock on exercise of stock options	538		538
Issuance of common stock on exercise of stock options (in shares)		212,740
Issuance of common stock under employee stock purchase plan (ESPP)	678		678
Issuance of common stock on employee stock purchase plan (ESPP) (in shares)		140,947
Sale of common stock in a private placement, net of issuance costs	32,093	$ 6	32,087
Sale of common stock in a private placement, net of issuance costs (in shares)		5,723,300
Stock-based compensation expense (employee)	6,046		6,046
Stock-based compensation expense (non-employee)	15		15
Stock-based compensation expense (ESPP)	317		317
Net loss	(31,358)			(31,358)
Net loss and comprehensive loss	(31,358)
Balance at Dec. 31, 2016	59,581	$ 34	239,631	(180,084)
Balance (in shares) at Dec. 31, 2016		33,762,278
Increase (Decrease) in Stockholders' Equity [Rollforward]
Issuance of common stock on exercise of stock options and vesting of restricted stock units	1,374		1,374
Issuance of common stock on exercise of stock options and vesting of restricted stock units (in shares)		295,059
Issuance of common stock under employee stock purchase plan (ESPP)	656		656
Issuance of common stock on employee stock purchase plan (ESPP) (in shares)		153,051
Stock-based compensation expense (employee)	6,352		6,352
Stock-based compensation expense (non-employee)	19		19
Stock-based compensation expense (ESPP)	246		246
Net loss	(31,003)			(31,003)
Net loss and comprehensive loss	(31,003)
Balance at Dec. 31, 2017	$ 37,225	$ 34	248,278	(211,087)
Balance (in shares) at Dec. 31, 2017		34,210,388
Increase (Decrease) in Stockholders' Equity [Rollforward]
Issuance of common stock on exercise of stock options (in shares)	740,010
Issuance of common stock on exercise of stock options and vesting of restricted stock units	$ 3,433	$ 1	3,432
Issuance of common stock on exercise of stock options and vesting of restricted stock units (in shares)		756,231
Issuance of common stock under employee stock purchase plan (ESPP)	790		790
Issuance of common stock on employee stock purchase plan (ESPP) (in shares)		146,583
Sale of common stock in a private placement, net of issuance costs	55,038	$ 6	55,032
Sale of common stock in a private placement, net of issuance costs (in shares)		5,750,000
Stock-based compensation expense (employee)	5,602		5,602
Stock-based compensation expense (non-employee)	24		24
Stock-based compensation expense (ESPP)	332		332
Legal settlement from short-swing profits, net of tax	310		310
Net loss	(22,999)			(22,999)
Net loss and comprehensive loss	(22,999)
Balance at Dec. 31, 2018	$ 79,755	$ 41	$ 313,800	$ (234,086)
Balance (in shares) at Dec. 31, 2018		40,863,202

Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Common stock private placement costs	$ 3,890	$ 2,247

Statements of Cash Flows $ in Thousands	12 Months Ended
Statements of Cash Flows $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Operating activities
Net loss	$ (22,999)	$ (31,003)	$ (31,358)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,920	3,841	3,511
Bad debt expense	0	0	68
Loss on disposal of property and equipment	0	12	12
Genzyme co-promotion fee amortization	0	0	(948)
Stock-based compensation	5,958	6,617	6,378
Other income	(93)	0	0
Conversion of accrued interest to long-term debt	0	0	385
Amortization and write-off of debt discount and issuance costs	32	472	173
Interest on end-of-term debt obligation and prepayment penalty	312	1,589	206
Changes in operating assets and liabilities:
Accounts receivable	(452)	(3,960)	(5,321)
Supplies	1,922	(1,849)	292
Prepaid expenses and other current assets	(517)	(7)	(415)
Other assets	(760)	(192)	25
Accounts payable	(1,568)	1,728	(1,441)
Accrued liabilities and deferred rent	724	(1,163)	451
Net cash used in operating activities	(13,521)	(23,915)	(27,982)
Investing activities
Purchases of property and equipment	(1,874)	(1,755)	(4,210)
Proceeds from the sale of property and equipment	0	440	0
Net cash used in investing activities	(1,874)	(1,315)	(4,210)
Financing activities
Proceeds from the issuance of long-term debt, net of debt issuance costs	0	24,880	24,452
Proceeds from issuance of common stock in a public offering, net of issuance costs	55,038	200	31,949
Payment of long-term debt	0	(25,385)	(5,000)
Payment of end-of-term debt obligation and prepayment penalty	0	(1,536)	(288)
Proceeds from legal settlement regarding short-swing profits	403	0	0
Payment of capital lease liability	(292)	(274)	0
Proceeds from the exercise of common stock options and employee stock purchases	4,350	1,897	1,216
Net cash provided by (used in) financing activities	59,499	(218)	52,329
Net increase (decrease) in cash, cash equivalents and restricted cash	44,104	(25,448)	20,137
Cash, cash equivalents and restricted cash at beginning of year	34,494	59,942	39,805
Cash, cash equivalents and restricted cash at end of year	78,598	34,494	59,942
Supplementary cash flow information of non-cash investing and financing activities:
Net receivable for reimbursement of public offering issuance costs	0	0	144
Purchases of property and equipment included in accounts payable and accrued liabilities	273	42	363
Supplementary cash flow information:
Cash paid for interest on debt	1,547	2,718	2,149
Cash paid for tax	79	21	7
Cash and cash equivalents	77,995	33,891	59,219
Restricted cash - current	0	0	120
Restricted cash - long-term	603	603	603
Total cash, cash equivalents and restricted cash	$ 78,598	$ 34,494	$ 59,942

Organization and Description of Business	12 Months Ended
Organization and Description of Business	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Veracyte, Inc. (“Veracyte” or the “Company”) is a genomic diagnostics company with a mission to improve diagnostic accuracy through innovation. The Company’s foundational science is enabling it to serve critical medical needs and expand its services further along the clinical continuum of care so that it can advance early detection of disease and inform treatment decisions at the same time as diagnosis. Veracyte was incorporated in the state of Delaware on August 15, 2006 as Calderome, Inc. Calderome operated as an incubator until early 2008. On March 4, 2008, the Company changed its name to Veracyte, Inc. The Company’s operations are based in South San Francisco, California and Austin, Texas, and it operates in one segment. Since the Company's founding in 2008, it has commercialized three products: Afirma Genomic Sequencing Classifier (GSC) and Xpression Atlas - The Company’s Afirma offering, consisting of the Afirma GSC and the Afirma Xpression Atlas, provides physicians with a comprehensive solution in thyroid nodule diagnosis. The combined offering is intended to provide physicians with clinically actionable results from a single fine needle aspiration (FNA) biopsy. The Afirma GSC was developed with RNA whole-transcriptome sequencing and machine learning, and is used to identify patients with benign thyroid nodules among those with indeterminate cytopathology results so that these patients can avoid unnecessary thyroid surgery. The Afirma Xpression Atlas provides physicians with genomic alteration content from the same FNA samples that are used in Afirma GSC testing and may help physicians decide with greater confidence on the surgical or therapeutic pathway for their patients. Percepta Bronchial Genomic Classifier - The Percepta classifier improves lung cancer diagnosis by enhancing the performance of diagnostic bronchoscopies, thus identifying more patients with lung nodules who are at low risk of cancer and may avoid further, invasive procedures. The test is built upon foundational "field of injury" science - through which genomic changes associated with lung cancer in current and former smokers can be identified with a simple brushing of a person's airway - without the need to sample the often hard-to-reach nodule directly. Envisia Genomic Classifier - The Envisia Genomic Classifier improves diagnosis of IPF by helping physicians better differentiate IPF from other interstitial lung diseases without the need for surgery. The test identifies the genomic pattern of usual interstitial pneumonia, a hallmark of IPF, with high accuracy on patient samples that are obtained through transbronchial biopsy, a nonsurgical procedure that is commonly used in lung evaluation. The Company’s clinical and scientific platform, which is used in the discovery and development of new products, also provides multiple opportunities for partnerships with biopharmaceutical companies. In developing the Company’s products, it has built or gained access to unique biorepositories that include extensive clinical cohorts and whole genome RNA sequencing data that it believes are important to the development of new targeted therapies, determining clinical trial eligibility and guiding treatment selection. All of the Company's testing services are made available through its clinical reference laboratories located in South San Francisco, California and Austin, Texas.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation

The Company's financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("U.S. GAAP").

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant items subject to such estimates include: revenue recognition; the useful lives of property and equipment; the recoverability of long-lived assets; the estimation of the fair value of intangible assets; stock options; income tax uncertainties, including a valuation allowance for deferred tax assets; and contingencies. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. These estimates form the basis for making judgments about the carrying values of assets and liabilities and recorded revenue and expenses that are not readily apparent from other sources. Actual results could differ from those estimates and assumptions.

Liquidity

The Company has incurred net losses since its inception and expects to incur additional losses in 2019 and in future years. As of December 31, 2018, the Company had an accumulated deficit of $234.1 million. The Company may never achieve revenue sufficient to offset its expenses. The Company believes its cash and cash equivalents of $78.0 million as of December 31, 2018 and its revenue from sales in 2019 will be sufficient to meet its anticipated cash requirements through at least February 2020.

In July 2018, the Company issued and sold 5,750,000 shares of common stock in a registered public offering, including the shares issued and sold upon the underwriters' exercise in full of their option to purchase an additional 750,000 shares, at a price to the public of $10.25 per share. The Company's net proceeds from the offering were approximately $55.0 million, after deducting underwriting commissions and offering expenses of $3.9 million.

In November 2017, the Company entered into a Loan and Security Agreement and drew down a term loan advance of $25.0 million of which the entire amount was used to pay the outstanding balance of the Company's previous long-term debt as discussed in Note 7 - Debt.

If the Company is not able to generate revenue to finance its cash requirements, the Company will need to finance future cash needs primarily through public or private equity offerings, debt financings, borrowings or strategic collaborations or licensing arrangements. If the Company is not able to secure additional funding when needed, on acceptable terms, it may have to delay, reduce the scope of or eliminate one or more research and development programs or selling and marketing initiatives which may have a material adverse effect on the Company's business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all.

Concentrations of Credit Risk and Other Risks and Uncertainties

The majority of the Company's cash and cash equivalents are deposited with one major financial institution in the United States. Deposits in this institution may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents.

Several of the components of the Company's sample collection kit and test reagents are obtained from single-source suppliers. If these single-source suppliers fail to satisfy the Company's requirements on a timely basis, it could suffer delays in being able to deliver its diagnostic solutions, a possible loss of revenue, or incur higher costs, any of which could adversely affect its operating results.

The Company is also subject to credit risk from its accounts receivable related to its sales. The Company does not perform evaluations of customers' financial condition and does not require collateral.

Through December 31, 2018, most of the Company's revenue have been derived from the sale of Afirma. To date, Afirma has been delivered primarily to physicians in the United States. The Company's third-party payers in excess of 10% of revenue and their related revenue as a percentage of total revenue were as follows:



	Year Ended December 31,
	2018		2017		2016
Medicare	29	%	26	%	27	%
UnitedHealthcare	12	%	14	%	12	%
	41	%	40	%	39	%

The Company's significant third-party payers in excess of 10% of accounts receivable and their related accounts receivable balance as a percentage of total accounts receivable were as follows:



	As of December 31,
	2018		2017
Medicare	20	%	22	%
UnitedHealthcare	11	%	9	%

Cash Equivalents

Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase. Cash equivalents consist of amounts invested in a money market account primarily consisting of U.S. Treasury reserves.

Restricted Cash

The Company had deposits of $603,000 included in long-term assets as of December 31, 2018 and December 31, 2017, restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit held as security for the lease of the Company's South San Francisco facility.

The Company adopted the FASB issued Accounting Standards Update ("ASU") No. 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash retrospectively as of January 1, 2018 and restricted cash and restricted cash equivalents are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The adoption of this ASU did not have a material impact on the Company's financial statements.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally between three and five years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the term of the lease. Maintenance and repairs are charged to expense as incurred, and improvements and betterments are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in the statements of operations and comprehensive loss in the period realized.

Finite-lived Intangible Assets

Finite-lived intangible assets consist of intangible assets reclassified from indefinite-lived intangible assets, following the launch of Percepta in April 2015. The Company amortizes finite-lived intangible assets using the straight-line method over their estimated useful life. The estimated useful life of 15 years was used for the intangible asset related to the Percepta test based on management's estimate of product life, product life of other diagnostic tests and patent life. The Company tests this finite-lived intangible asset for impairment when events or circumstances indicate a reduction in the fair value below its carrying amount. There was no impairment for the years ended December 31, 2018, 2017 or 2016.

Goodwill

Goodwill, derived from the Company's acquisition of Allegro Diagnostics Corp. in September 2014, is reviewed for impairment on an annual basis or more frequently if events or circumstances indicate that it may be impaired. The Company's goodwill evaluation is based on both qualitative and quantitative assessments regarding the fair value of goodwill relative to its carrying value. The Company has determined that it operates in a single segment and has a single reporting unit associated with the development and commercialization of diagnostic products. In the event the Company determines that it is more likely than not the carrying value of the reporting unit is higher than its fair value, quantitative testing is performed comparing recorded values to estimated fair values. If impairment is present, the impairment loss is measured as the excess of the recorded goodwill over its implied fair value. The Company performs its annual evaluation of goodwill during the fourth quarter of each fiscal year. There was no impairment for the years ended December 31, 2018, 2017 or 2016.

Fair Value of Financial Instruments

The carrying amounts of certain financial instruments including cash and cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.

See Note 5, "Fair Value Measurements" for further information on the fair value of the Company’s financial instruments.

Revenue Recognition

The Company commenced recognizing revenue in accordance with the provisions of ASC 606, Revenue from Contracts with Customers, or ASC 606, starting January 1, 2018. Prior to January 1, 2018, the Company recognized revenue in accordance with the provisions of ASC 954-605, Health Care Entities - Revenue Recognition, or ASC 954.

Revenue from Diagnostic Services

Most of the Company’s revenue is generated from the provision of diagnostic services. These services are completed upon the delivery of test results to the prescribing physician, at which time the Company bills for the services. The Company recognizes revenue related to billings based on estimates of the amount that will ultimately be realized. In determining the amount to accrue for a delivered test, the Company considers factors such as payment history, payer coverage, whether there is a reimbursement contract between the payer and the Company, payment as a percentage of agreed upon rate (if applicable), amount paid per test and any current developments or changes that could impact reimbursement. These estimates require significant judgment by management.

The Company adopted ASC 606 on January 1, 2018 using the modified retrospective method, which requires a cumulative catch-up adjustment as if the Company had recognized revenue under ASC 606 from January 1, 2016. Prior to January 1, 2018, the Company recognized revenue in accordance with ASC 954 and recognized revenue for tests delivered on an accrual basis when amounts that will ultimately be realized could be reasonably estimated, and on the cash basis when there was insufficient information to estimate revenue accruals. There was sufficient payment history for the Company to substantially accrue all revenue upon delivery of test results starting July 1, 2016 and the Company continued to recognize revenue in 2017 upon cash receipt for unaccrued tests that were delivered prior to July 1, 2016.

Revenue recognized for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands of dollars):



	Year Ended December 31,
	2018				2017				2016
Revenue recognized on the accrual basis	$	92,008	100	%	$	69,274	96	%	$	47,099	72	%
Revenue recognized on the cash basis	—		—	%	2,679		4	%	17,986		28	%
Total	$	92,008	100	%	$	71,953	100	%	$	65,085	100	%

As noted above, on July 1, 2016 the Company began recognizing revenue from substantially all its tests on the accrual basis of accounting at an amount equal to management’s best estimate of the cash to ultimately be collected. For tests delivered prior to July 1, 2016, substantially all the related cash had been collected by December 31, 2017. Thus, at January 1, 2018, the cumulative impact of adopting ASC 606 was not material and no adjustment was recorded. Since the Company commenced recognizing revenue from substantially all of its tests on the accrual basis of accounting commencing on July 1, 2016, and continued to do so after the adoption of ASC 606, the adoption of ASC 606 did not have a material impact on the Company's statement of operations for the year ended December 31, 2018.

During 2018, the Company changed its revenue estimates due to actual and anticipated cash collections for tests delivered in 2018 or prior quarters and recognized additional revenue of $2.0 million, of which $1.5 million had been collected as of December 31, 2018. This resulted in a decrease in the Company's loss from operations of $2.0 million and a decrease in loss per share of $0.05 for the year ended December 31, 2018.

Arrangements with multiple-performance obligations

From time to time, the Company enters into arrangements for the research and development and/or commercialization of services. Such arrangements may require us to deliver various rights, services and/or samples, including intellectual property rights/licenses, R&D services, and/or commercialization of services. The underlying terms of these arrangements generally provide for consideration to the Company in the form of nonrefundable upfront license fees, development and commercial performance milestone payments, royalty payments and/or profit sharing.

In arrangements involving more than one performance obligation, each required performance obligation is evaluated to determine whether it qualifies as a distinct performance obligation based on whether (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available and (ii) the good or service is separately identifiable from other promises in the contract. The consideration under the arrangement is then allocated to each separate distinct performance obligation based on its respective relative stand-alone selling price. The estimated selling price of each deliverable reflects our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis or using an adjusted market assessment approach if selling price on a stand-alone basis is not available.

The consideration allocated to each distinct performance obligation is recognized as revenue when control of the related goods or services is transferred. Consideration associated with at-risk substantive performance milestones is recognized as revenue when it is probable that a significant reversal of the cumulative revenue recognized will not occur. Should there be royalties, the Company utilizes the sales and usage-based royalty exception in arrangements that resulted from the license of intellectual property, recognizing revenues generated from royalties or profit sharing as the underlying sales occur.

Biopharmaceutical Services

On April 9, 2018, the Company entered into an agreement with a biopharmaceutical company whereby the Company agreed to provide certain tissue samples and other services in exchange for agreed-upon fees. During the quarter ended June 30, 2018, the Company recognized $450,000 of revenue upon deliveries of tissue samples and the Company received $500,000 for other services, which was recognized ratably during the quarters ended September 30 and December 31, 2018 as the services were performed. Thereafter, the Company expects to receive approximately $250,000 per quarter as services are performed and may also recognize revenue related to the deliveries of additional tissue samples as long as the agreement is not terminated. The agreement has a one-year term with an automatic renewal of one year and the biopharmaceutical company may terminate the agreement at any time with at least 90 days' notice. The Company evaluated the accounting for this agreement under ASC 606 and concluded that the performance obligations thereunder are the deliveries of tissue samples and performance of services, both of which are distinct. For the year ended December 31, 2018, the Company recognized revenue of $450,000 for the deliveries of tissue samples and $500,000 for performance of services. There was no deferred revenue related to this agreement at December 31, 2018.

Collaboration with Johnson & Johnson

On December 28 2018, the Company entered into an agreement with Johnson & Johnson Services, Inc. (JJSI) whereby the Company agreed to provide data to JJSI for the development of their products and JJSI would provide samples and data to the Company to advance the development and commercialization of novel diagnostic tests to detect lung cancer. There are also associated milestones and royalties. As of December 31, 2018, there were no performance of obligations under the agreement or consideration paid. The agreement will be accounted for under our policy on arrangements with multiple-performance obligations mentioned in the footnote above.

Cost of Revenue

The components of our cost of revenue are laboratory expenses, sample collection expenses, compensation expense, license fees and royalties, depreciation and amortization, other expenses such as equipment and laboratory supplies, and allocations of facility and information technology expenses. Costs associated with performing tests are expensed as the test is processed regardless of whether and when revenue is recognized with respect to that test.

Research and Development

Research and development expenses include expenses incurred to develop our technology, collect clinical samples and conduct clinical studies to develop and support our products. These expenses consist of compensation expenses, direct research and development expenses such as prototype materials, laboratory supplies and costs associated with setting up and conducting clinical studies at domestic and international sites, professional fees, depreciation and amortization, other miscellaneous expenses and allocation of facility and information technology expenses. We expense all research and development costs in the periods in which they are incurred.

Income Taxes

The Company accounts for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized.

The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. The Company's assessment of an uncertain tax position begins with the initial determination of the position's sustainability and is measured at the largest amount of benefit that is more-likely-than-not of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit may change as new information becomes available.

Stock-based Compensation

Stock-based compensation expense for equity instruments issued to employees is measured based on the grant-date fair value of the awards. The fair value of each employee stock option is estimated on the date of grant using the Black-Scholes option-pricing model. The Company recognizes compensation costs on a straight-line basis for all employee stock-based compensation awards that are expected to vest over the requisite service period of the awards, which is generally the awards' vesting period. Forfeitures are required to be estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates.

Following the adoption of ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share Based Payment Accounting by the Company on October 1, 2018, stock-based compensation expense for equity instruments issued to non-employees is also measured based on the grant-date fair value of the awards using the Black-Scholes option-pricing model. Prior to this, the fair value of such awards was subject to re-measurement as the underlying equity awards vest.

Net Loss per Common Share

Basic net loss per common share is calculated by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury stock method. Potentially dilutive securities consisting of options to purchase common stock, restricted stock units and shares subject to purchase under our employee stock purchase plan are considered to be common stock equivalents and were excluded from the calculation of diluted net loss per common share because their effect would be anti-dilutive for all periods presented.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU No. 2016-2, Leases (Topic 842). This ASU is aimed at making leasing activities more transparent and comparable, and requires substantially all leases be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. The ASU will be effective for interim and annual periods beginning after December 15, 2018. Additionally, the FASB issued ASU, No. 2018-11, Leases (Topic 842): Targeted Improvements, which offers an additional transition method whereby entities may apply the new leases standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings rather than application of the new leases standard at the beginning of the earliest period presented in the financial statements. The Company adopted this standard on January 1, 2019 and has performed an analysis on the impact of this standard and does not expect that this standard will have a material impact on its results of operations or cash flows, but that it will have a material impact on the Company’s assets and liabilities.

In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share Based Payment Accounting. Under this ASU, the accounting for share-based payments to nonemployees and employees will be substantially aligned, primarily by permitting the measurement of nonemployee awards to be fixed at the grant date. This ASU is effective for all interim and annual reporting periods beginning on or after December 15, 2018, with early adoption permitted. The Company adopted this ASU on October 1, 2018 using the modified retrospective method. The adoption of the ASU did not result in a cumulative-effect adjustment or have a material impact on the Company's financial position or results of operations.

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808). Under this ASU, transactions in collaborative arrangements are to be accounted for under ASC 606 if the counterparty is a customer for a good or service (or bundle of goods and services) that is a distinct unit of account. Also, entities are precluded from presenting consideration from transactions with a counterparty that is not a customer together with revenue recognized from ASC 606. This ASU is effective for all interim and annual reporting periods beginning on or after December 15, 2019, with early adoption permitted. The Company is currently evaluating the potential effect of this standard on its financial statements.

Net Loss Per Share

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Net Loss Per Share

The following outstanding common stock equivalents have been excluded from diluted net loss per common share for the years ended December 31, 2018, 2017 and 2016 because their inclusion would be anti-dilutive:



	Year Ended December 31,
	2018	2017	2016
Shares of common stock subject to outstanding options	5,998,163	6,163,734	5,093,454
Employee stock purchase plan	34,869	34,559	36,651
Restricted stock units	384,691	63,425	25,000
Total common stock equivalents	6,417,723	6,261,718	5,155,105

Balance Sheet Components

12 Months Ended

Dec. 31, 2018

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

Property and Equipment, Net

Property and equipment consisted of the following (in thousands of dollars):



	December 31,
	2018			2017
Leasehold improvements	$	5,825		$	5,790
Laboratory equipment	8,895			8,026
Computer equipment	1,615			1,293
Software, including software developed for internal use	2,450			2,308
Furniture and fixtures	1,435			1,435
Construction-in-process	726			141
Total property and equipment, at cost	20,946			18,993
Accumulated depreciation and amortization	(12,006		)	(9,305		)
Total property and equipment, net	$	8,940		$	9,688

Depreciation and amortization expense was $2.9 million, $2.8 million and $2.4 million for the years ended December 31, 2018, 2017 and 2016, respectively.

The Company has a capital lease for laboratory equipment that went into service in 2017 with a cost of $1.2 million, accumulated depreciation of $367,000 and $135,000 at December 31, 2018 and 2017, respectively and depreciation of $232,000 and $135,000 for the years ended December 31, 2018 and 2017, respectively.

Finite-lived Intangible Assets

Amortization of the Percepta test intangible asset, which was acquired from the acquisition of Allegro in September 2014, began in April 2015 when research and development activities were deemed to be completed and is recognized on a straight-line basis. The amortization period of this intangible asset is over its estimated useful life of 15 years after taking into consideration expected use of the asset, legal or regulatory provisions that may limit or extend the life of the asset, as well as the effects of obsolescence and other economic factors. Amortization of $1.1 million was recognized for each of the years ended December 31, 2018, 2017, and 2016, respectively, and accumulated amortization was $4.0 million, $3.0 million, and $1.9 million as of December 31, 2018, 2017, and 2016, respectively. Amortization expense will be approximately $1.1 million per year over the remaining life of the asset.

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands of dollars):



	December 31,
	2018		2017
Accrued compensation expense	$	6,412	$	5,293
Accrued other	2,774		2,882
Total accrued liabilities	$	9,186	$	8,175

Fair Value Measurements

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company records its financial assets and liabilities at fair value. The carrying amounts of certain financial instruments of the Company, including cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. The carrying value of the Company's debt approximates its fair value because the interest rate approximates market rates that the Company could obtain for debt with similar terms. The fair value of the Company’s debt is estimated using the net present value of the payments, discounted at an interest rate that is consistent with market interest rates, which is a Level II input. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value, and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows:


•	Level I: Inputs which include quoted prices in active markets for identical assets and liabilities;


•	Level II: Inputs other than Level I that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and


•	Level III: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The fair value of the Company's financial assets includes money market funds and a deposit for the lease of the Company's South San Francisco facility. Money market funds, included in cash and cash equivalents in the accompanying balance sheets, was $76.6 million and $33.1 million as of December 31, 2018 and 2017, respectively, and are Level I assets as described above. The deposit for the lease, included in restricted cash in the accompanying balance sheets, was $603,000 as of December 31, 2018 and 2017, and is a Level I asset as described above.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Operating Leases

The Company leases its headquarters and laboratory facilities in South San Francisco, California under a non-cancelable lease agreement for approximately 59,000 square feet. The lease began in June 2015 and ends in March 2026 and contains extension of lease term and expansion options. In February 2017, the Company relinquished certain expansion rights for a nominal fee. The Company had deposits of $603,000 included in long-term assets as of December 31, 2018 and 2017, restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit held as security for the lease of the South San Francisco facility.

The Company also leases laboratory and office space in Austin, Texas under a lease that expires in January 2029 and includes options for expansion and early termination in 2025. The Company provided a cash security deposit for this lease of $139,000, included in other assets in the Company's balance sheets as of December 31, 2018 and 2017.

Future minimum lease payments under non-cancelable operating leases as of December 31, 2018 are as follows (in thousands of dollars):



Year Ending December 31,	Amounts
2019	$	2,227
2020	2,332
2021	2,401
2022	2,472
2023	2,543
Thereafter	6,840
Total minimum lease payments	$	18,815

The Company recognizes rent expense on a straight-line basis over the non-cancelable lease period. Rent expense was $1.9 million, $1.9 million, and $2.0 million for the years ended December 31, 2018, 2017 and 2016, respectively.

Capital Lease

The Company entered into a capital lease in December 2016 for $1.2 million of laboratory equipment. The Company paid an upfront amount of $330,000 and the present value of the total future minimum lease payments at inception was $874,000. As at December 31, 2018, the annual future minimum payments under this lease are $317,000 for 2019.

Supplies Purchase Commitments

The Company had non-cancelable purchase commitments with suppliers to purchase a minimum quantity of supplies for approximately $7.3 million at December 31, 2018.

Contingencies

From time to time, the Company may be involved in legal proceedings arising in the ordinary course of business. The Company believes there is no litigation pending that could have, either individually or in the aggregate, a material impact on the Company's financial statements.

Debt

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Debt

Loan and Security Agreement

On November 3, 2017, the Company entered into a loan and security agreement (the “Loan and Security Agreement”) with Silicon Valley Bank. The Loan and Security Agreement allows the Company to borrow up to $35.0 million, with a $25.0 million advance term loan (the “Term Loan Advance”) and a revolving line of credit of up to $10.0 million (the “Revolving Line of Credit”). The Term Loan Advance was advanced upon the closing of the Loan and Security Agreement and was used to pay the outstanding balance of the Company’s existing long-term debt, which was canceled at that date. The Company had not drawn on the Revolving Line of Credit as of December 31, 2018. Borrowings under the Loan and Security Agreement mature on October 1, 2022. Amounts may be borrowed and repaid under the Revolving Line of Credit up until the earliest of full repayment or maturity of the Loan and Security Agreement, termination of the Loan and Security Agreement, or October 1, 2022.

The Term Loan Advance bears interest at a variable rate equal to (i) the thirty-day U.S. London Interbank Offer Rate (“LIBOR”) plus (ii) 4.20%, with a minimum rate of 5.43% per annum. Principal amounts outstanding under the Revolving Line of Credit bear interest at a variable rate equal to (i) LIBOR plus (ii) 3.50%, with a minimum rate of 4.70% per annum. The effective interest rate was 8.31% as of December 31, 2018.

The Company may prepay the outstanding principal amount under the Term Loan Advance plus accrued and unpaid interest and, if the Term Loan Advance is repaid in full, a prepayment premium. The prepayment premium will be (i) $750,000 if prepayment is made prior to November 3, 2018, (ii) $500,000 if the prepayment is made after November 3, 2018 but on or before November 3, 2019, or (iii) $250,000 if the prepayment is made after November 3, 2019. See Note 14, Subsequent Event.

In addition, a final payment on the Term Loan Advance in the amount of $1.2 million is due upon the earlier of the maturity date of the Term Loan Advance or its payment in full. The Loan and Security Agreement contains customary representations, warranties, and events of default such as a material adverse change in our business, operations or financial condition, as well as affirmative and negative covenants. The negative covenants include, among other provisions, covenants that limit or restrict the Company's ability to incur liens, make investments, incur indebtedness, merge with or acquire other entities, dispose of assets, make dividends or other distributions to holders of its equity interests, engage in any new line of business, or enter into certain transactions with affiliates, in each case subject to certain exceptions. The Company’s obligations under the Loan and Security Agreement are secured by substantially all of its assets (excluding intellectual property), subject to certain customary exceptions. The Loan and Security Agreement also requires the Company to achieve certain revenue levels tested quarterly on a trailing twelve-month basis. However, failure to maintain the revenue levels will not be considered a default if the Company maintains liquidity of at least $40.0 million. As of December 31, 2018, the Company was in compliance with the loan covenants.

As of December 31, 2018 and 2017, the net debt obligation for borrowings made under the Loan and Security Agreement was as follows (in thousands of dollars):



	December 31,
	2018			2017
Debt principal	$	25,000		$	25,000
End-of-term debt obligation	365			53
Unamortized debt issuance costs	(83		)	(115		)
Net debt obligation	$	25,282		$	24,938

Future principal and end-of-term debt obligation payments due under the Loan and Security Agreement are as follows (in thousands of dollars):



Year Ending December 31,
2019	$	1,389
2020	8,333
2021	8,333
2022	8,132
Total	$	26,187

The end-of-term debt obligation accretes over the term of the Loan and Security Agreement until maturity and is included in interest expense in the Company's statement of operations and comprehensive loss.

The current portion of long-term debt for the Loan and Security Agreement on the balance sheet as of December 31, 2018 includes $32,000 for unamortized debt issuance costs.

Credit Agreement

In March 2016, the Company entered into a credit agreement (the “Credit Agreement”) with Visium Healthcare Partners, LP (“Visium”). Under the Credit Agreement, two term loans were available to the Company with an aggregate principal amount of up to $40.0 million. The Company drew down the initial $25.0 million term loan (the “Initial Term Loan”) on March 30, 2016, of which $5.0 million was used to pay the outstanding balance of the Company’s previous long-term debt, which was canceled at that date.

The Term Loans bore interest at a fixed rate of 12.0% per annum and no principal payments were due through March 31, 2020. The Company was obligated to repay the outstanding principal amounts under the Term Loans in eight equal installments during the final two years under the Credit Agreement. Prepayment of the outstanding principal amount under the Term Loans prior to March 31, 2018 was subject to a prepayment premium equal to 24.0% of the outstanding principal balance, less the aggregate amount of all interest payments in cash. For any quarterly interest payment through and including the 16th interest payment date after the Initial Borrowing Date, so long as no event of default had occurred and was then continuing, the Company could have elected to pay interest in cash on the outstanding principal amounts of the Term Loans at a fixed rate of 9.0%, with the remaining 3.0% of the 12.0% interest paid-in-kind by adding such paid-in-kind interest to the outstanding principal amounts of the Term Loans. The Company elected to pay interest in-kind for the quarters ended June 30, 2016 and September 30, 2016, totaling $385,000.

As noted above, upon entering into the Loan and Security Agreement, the Credit Agreement was paid in full and terminated on November 3, 2017, wherein all commitments were terminated, all liens were released and all outstanding principal, interest and fees accrued thereunder were repaid in the aggregate amount of $27.3 million, including a prepayment premium of $1.5 million.

Interest Expense

Interest expense was recognized as follows (in thousands of dollars):



	Year Ended December 31,
	2018		2017		2016
Nominal debt interest	$	1,568	$	2,838	$	2,378
Amortization and write-off of debt discount and issuance costs	57		472		173
End-of-term debt obligation interest	312		53		156
Debt prepayment penalty	—		1,536		50
Interest on capital lease	26		42		—
Total	$	1,963	$	4,941	$	2,757

Stockholders' Equity

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Stockholders' Equity

Common Stock

The Company's Restated Certificate of Incorporation authorizes the Company to issue 125,000,000 shares of common stock with a par value of $0.001 per share. The holder of each share of common stock shall have one vote for each share of stock. The common stockholders are also entitled to receive dividends whenever funds and assets are legally available and when declared by the Board of Directors, subject to the prior rights of holders of all series of convertible preferred stock outstanding. No dividends have been declared as of December 31, 2018.

As of December 31, 2018 and 2017, the Company had reserved shares of common stock for issuance as follows:



	December 31,
	2018	2017
Stock options and restricted stock units issued and outstanding	6,235,258	6,061,081
Stock options and restricted stock units available for grant under stock option plans	1,571,658	1,133,907
Common stock available for the Employee Stock Purchase Plan	309,419	456,002
Total	8,116,335	7,650,990

In July 2018, the Company issued and sold 5,750,000 shares of common stock in a registered public offering, including the underwriters' exercise in full of their option to purchase an additional 750,000 shares, at a price to the public of $10.25 per share. The Company's net proceeds from the offering were $55.0 million, after deducting underwriting commissions and offering expenses of $3.9 million.

In November 2016, the Company issued and sold 5,723,300 shares of its common stock in a registered public offering, including the underwriters' exercise in full of their option to purchase an additional 750,000 shares, at a price of $6.00 per share. The Company's net proceeds from the offering were $32.1 million, after deducting underwriting commissions and offering expenses of $2.2 million. At December 31, 2016, the Company had $200,000 receivable from the underwriters for reimbursement of other expenses, which is included in prepaid expenses and other current assets in the Company's balance sheet at that date and received by the Company in 2017.

Stock Incentive Plans

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Incentive Plans

Stock Plans

In February 2008, the Company adopted the 2008 Stock Plan (the "2008 Plan"). The 2008 Plan provides for the granting of options to purchase common stock and common stock to employees, directors and consultants of the Company. The Company may grant incentive stock options ("ISOs"), non-statutory stock options ("NSOs") or restricted stock under the 2008 Plan. ISOs may only be granted to Company employees (including directors who are also considered employees). NSOs and restricted stock may be granted to Company employees, directors and consultants. Options may be granted for terms of up to ten years from the date of grant, as determined by the Board of Directors, provided however, that with respect to an ISO granted to a person who owns stock representing more than 10% of the voting power of all classes of stock of the Company, the term shall be for no more than five years from the date of grant. The exercise price of options granted must be at a price no less than 100% of the estimated fair value of the shares on the date of grant, as determined by the Board of Directors, provided however, that with respect to an ISO granted to an employee who at the time of grant of such option owns stock representing more than 10% of the voting power of all classes of stock of the Company, the exercise price shall not be less than 110% of the estimated fair value of the shares on the date of grant.

In October 2013, the Company adopted the 2013 Stock Incentive Plan (the "2013 Plan"). The 2013 Plan was subsequently approved by the Company's stockholders and became effective on November 4, 2013, immediately before the closing of the Company's initial public offering ("IPO"). Following the effectiveness of the 2013 Plan, no additional options were granted under the 2008 Plan. An aggregate of 1,700,000 shares were initially reserved for issuance under the 2013 Plan. In addition, to the extent that any awards outstanding or subject to vesting restrictions under the 2008 Plan are subsequently forfeited or terminated for any reason before being exercised or settled, the shares of common stock reserved for issuance pursuant to such awards as of the closing of the IPO will become available for issuance under the 2013 Plan. The remaining shares available for grant under the 2008 Plan became available for issuance under the 2013 Plan upon the closing of the IPO. On the first day of each year from 2014 to 2023, the 2013 Plan authorizes an annual increase of the lesser of 4% of outstanding shares on the last day of the immediately preceding fiscal year or a lesser amount as determined by the Company's Board of Directors. As of December 31, 2018, 1,571,658 shares were available for future issuance under the 2013 Plan.

Pursuant to the 2013 Plan, stock options, restricted shares, stock units, including restricted stock units and stock appreciation rights may be granted to employees, consultants, and outside directors of the Company. Options granted may be either ISOs or NSOs.

Stock options are governed by stock option agreements between the Company and recipients of stock options. ISOs and NSOs may be granted under the 2013 Plan at an exercise price of not less than 100% of the fair market value of the common stock on the date of grant, determined by the Compensation Committee of the Board of Directors. Options become exercisable and expire as determined by the Compensation Committee, provided that the term of ISOs may not exceed ten years from the date of grant. Stock option agreements may provide for accelerated exercisability in the event of an optionee's death, disability, or retirement or other events.

Stock units are governed by stock unit agreements between the Company and recipients of stock units. Stock units may be granted under the 2013 Plan and the number of stock units awarded are determined by the Compensation Committee of the Board of Directors. Stock units vest and expire as determined by the Compensation Committee. Stock unit agreements may provide for accelerated vesting in the event of a stock unit holder's death, disability, or retirement or other events.

Any outside director who was not previously an employee and who first joins the Company's Board of Directors on or after the effective date of the 2013 Plan will be automatically granted an initial NSO to purchase 35,000 shares of common stock upon first becoming a member of the Board of Directors. The shares subject to the initial option will vest and become exercisable one-third (1/3) each of the first, second and third annual anniversaries of the date of grant. On the first business day after each regularly scheduled annual meeting of stockholders, each outside director who was not elected to the Board of Directors for the first time at such meeting and who will continue serving as a member of the Board of Directors thereafter will be automatically granted an option to purchase 10,000 shares of common stock, provided that the outside director has served on the Board of Directors for at least six months. Each annual option will vest and become exercisable on the first anniversary of the date of grant, or immediately prior to the next regular annual meeting of the Company's stockholders following the date of grant if the meeting occurs prior to the first anniversary date. The options granted to outside directors will have a per share exercise price equal to 100% of the fair market value of the underlying shares on the date of grant and will become fully vested in the event of a change of control. In addition, such options will terminate on the earlier of (i) the day before the 10th anniversary of the date of grant or (ii) the date 12 months after the termination of the outside director's service for any reason.

The following table summarizes activity under the Company's stock incentive plans (aggregate intrinsic value in thousands):



	Shares Available for Grant		Stock Options Outstanding and Unvested Stock Units		Weighted Average Exercise Price of Stock Options		Weighted Average Remaining Contractual Life of Stock Options (Years)	Aggregate Intrinsic Value of Stock Options
Balance—December 31, 2017	1,133,907		6,061,081		$	7.76	6.71	$	4,531
Additional shares authorized	1,368,159		—
Granted - stock options	(1,126,750	)	1,126,750		7.08
Granted - restricted stock units	(590,420	)	590,420
Canceled	779,982		(779,982	)	8.00
Exercised	—		(740,010	)	4.71
Restricted stock units vested	—		(23,001	)
Tax portion of restricted stock units vested	6,780		—
Balance—December 31, 2018	1,571,658		6,235,258		$	7.95	6.95	$	27,340

Options vested and exercisable—December 31, 2018			3,341,576		$	8.22	5.87	$	15,829
Options vested and expected to vest—December 31, 2018			5,406,347		$	7.96	6.87	$	26,238

The aggregate intrinsic value was calculated as the difference between the exercise price of the options to purchase common stock and the fair market value of the Company's common stock, which was $12.58 and $6.53 per share as of December 31, 2018 and 2017, respectively.

The weighted average fair value of options to purchase common stock granted was $3.62, $4.49 and $3.35 for the years ended December 31, 2018, 2017 and 2016, respectively.

The aggregate estimated grant date fair value of employee options to purchase common stock vested during the years ended December 31, 2018, 2017 and 2016 was $4.1 million, $3.1 million and $5.8 million, respectively.

The intrinsic value of stock options exercised was $4.9 million, $0.7 million and $0.9 million for the years ended December 31, 2018, 2017 and 2016, respectively.

The weighted average fair value of restricted stock units granted was $6.17 and $8.93 for the years ended December 31, 2018 and 2017, respectively. The intrinsic value of restricted stock units vested was $184,000 and $157,000 for the years ended December 31, 2018 and 2017, respectively.

Employee Stock Purchase Plan

In May 2015, the Company's stockholders approved the Company's ESPP. The ESPP provides eligible employees with an opportunity to purchase common stock from the Company and to pay for their purchases through payroll deductions. The ESPP will be implemented through a series of offerings of purchase rights to eligible employees. Under the ESPP, the Compensation Committee of the Company's Board of Directors may specify offerings with a duration of not more than 12 months, and may specify shorter purchase periods within each offering. During each purchase period, payroll deductions will accumulate, without interest. On the last day of the purchase period, accumulated payroll deductions will be used to purchase common stock for employees participating in the offering.

The purchase price will be specified pursuant to the offering, but cannot, under the terms of the ESPP, be less than 85% of the fair market value per share of the Company's common stock on either the offering date or on the purchase date, whichever is less.

The Company's Board of Directors has determined that the purchase periods initially shall have a duration of six months, that the first purchase period began on August 3, 2015 and that the purchase price will be 85% of the fair market value per share of the Company's common stock on either the offering date or the purchase date, whichever is less. The length of the purchase period applicable to U.S. employees and the purchase price may not be changed without the approval of the independent members of the Compensation Committee of the Company's Board of Directors. The Compensation Committee has determined that if the fair market value of a share of the Company's common stock on any purchase date within a particular offering period is less than the fair market value on the start date of that offering period, then the offering period will automatically terminate and the employees in that offering period will automatically be transferred and enrolled in a new offering period which will begin on the next day following such purchase date.

No employee is permitted to accrue, under the ESPP, a right to purchase stock of the Company having a value in excess of $25,000 of the fair market value of such stock (determined at the time the right is granted) for each calendar year.

Stock-based Compensation

The following table summarizes stock-based compensation expense related to stock options, restricted stock units and the ESPP for the years ended December 31, 2018, 2017 and 2016, and are included in the statements of operations and comprehensive loss as follows (in thousands of dollars):



	Year Ended December 31,
	2018		2017		2016
Cost of revenue	$	130	$	133	$	126
Research and development	1,018		1,495		1,322
Selling and marketing	1,866		1,899		1,594
General and administrative	2,944		3,090		3,336
Total stock-based compensation expense	$	5,958	$	6,617	$	6,378

As of December 31, 2018, the Company had $9.1 million of unrecognized compensation expense related to unvested stock options and restricted stock units, which is expected to be recognized over an estimated weighted-average period of 2.30 years.

The estimated grant-date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Weighted-average volatility	50.40 - 52.70%	50.40 - 52.40%	52.49 - 56.36%
Weighted-average expected term (years)	5.50 - 6.08	5.50 - 6.08	5.50 - 6.27
Risk-free interest rate	2.40 - 3.10%	1.80 - 2.33%	1.16 - 2.09%
Expected dividend yield	—	—	—

The estimated fair value of non-employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Weighted-average volatility	43.60 - 50.50%	50.40 - 51.10%	52.77 - 65.85%
Weighted-average expected term (years)	0.25 - 6.75	6.80 - 7.75	7.80 - 8.56
Risk-free interest rate	1.84 - 2.87%	2.16 - 2.37%	1.39 - 2.30%
Expected dividend yield	—	—	—

The estimated grant date fair value of the ESPP shares was calculated using the Black-Scholes option-pricing model, based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Weighted-average volatility	42.88 - 47.74%	37.00 - 43.86%	46.38 - 75.72%
Weighted-average expected term (years)	0.50 - 1.00	0.50 - 1.00	0.50 - 1.00
Risk-free interest rate	1.64 - 2.45%	0.65 - 1.22%	0.40 - 0.50%
Expected dividend yield	—	—	—

Genzyme Co-Promotion Agreement	12 Months Ended
Genzyme Co-Promotion Agreement	Dec. 31, 2018
Genzyme Co-Promotion Agreement
Genzyme Co-Promotion Agreement	Genzyme Co-Promotion Agreement In January 2012, the Company and Genzyme Corporation ("Genzyme") executed a co-promotion agreement for the co-exclusive rights and license to promote and market the Company's Afirma thyroid diagnostic solution in the United States and in 40 named countries. In exchange, the Company received a $10.0 million upfront co-promotion fee from Genzyme in February 2012 that was recognized on a straight-line basis over the term of the agreement. Under the terms of the co-promotion agreement, Genzyme received a percentage of U.S. cash receipts that the Company has received related to Afirma as co-promotion fees. The agreement was terminated effective September 9, 2016 with the remaining portion of the upfront co-promotion fee recognized through that date. In February 2015, the Company entered into an ex-U.S. co-promotion agreement with Genzyme for the promotion of the Afirma solution test with exclusivity in five countries outside the United States initially and in other countries agreed to from time to time. The agreement commenced on January 1, 2015 and effective July 6, 2017, was terminated. Payments made under this agreement for all periods presented were not material. The Company incurred $6.1 million in co-promotion expense, excluding the amortization of the upfront co-promotion fee, in the year ended December 31, 2016, which is included in selling and marketing expenses in the statements of operations and comprehensive loss. The Company had no obligation to Genzyme at either December 31, 2018 or December 31, 2017. The Company amortized $0.9 million of the $10.0 million upfront co-promotion fee in the year ended December 31, 2016, which is reflected as a reduction to selling and marketing expenses in the accompanying statements of operations and comprehensive loss. The upfront fee was fully amortized in 2016.

Thyroid Cytopathology Partners	12 Months Ended
Thyroid Cytopathology Partners	Dec. 31, 2018
Thyroid Cytopathology Partners
Thyroid Cytopathology Partners	Thyroid Cytopathology Partners In 2010, the Company entered into an arrangement with Pathology Resource Consultants, P.A. ("PRC") to set up and manage a specialized pathology practice to provide testing services to the Company. There was no direct monetary compensation from the Company to PRC as a result of this arrangement. The Company's service agreement is with the specialized pathology practice, Thyroid Cytopathology Partners, ("TCP"), which was managed by PRC and was effective through December 31, 2015, and thereafter automatically renews every year unless either party provides notice of intent not to renew at least 12 months prior to the end of the then-current term. Under the service agreement, the Company pays TCP based on a fixed price per test schedule, which is reviewed periodically for changes in market pricing. Subsequent to December 2012, an amendment to the service agreement allows TCP to sublease a portion of the Company's facility in Austin, Texas. The Company does not have an ownership interest in or provide any form of financial or other support to TCP. The Company has concluded that TCP represents a variable interest entity and that the Company is not the primary beneficiary as it does not have the ability to direct the activities that most significantly impact TCP's economic performance. Therefore, the Company does not consolidate TCP. All amounts paid to TCP under the service agreement are expensed as incurred and included in cost of revenue in the accompanying statements of operations and comprehensive loss. On October 16, 2017, the Company amended and restated its service agreement with TCP. The agreement is effective through October 31, 2022, and thereafter automatically renews every year unless either party provides notice of intent not to renew at least 12 months prior to the end of the then-current term. In connection with amending and restating the TCP agreement, the Company’s arrangement with PRC was simultaneously assigned by PRC to TCP and immediately terminated, and the Company agreed to pay PRC a total of $1.8 million over eight quarterly installments in exchange for TCP reducing the price per test it charges the Company during the term of the amended TCP agreement. Payments are amortized over the term of the agreement and included in cost of revenue in the Company's statement of operations and comprehensive loss. The Company incurred $3.9 million, $4.6 million, and $5.1 million for the years ended December 31, 2018, 2017 and 2016, respectively, in cytopathology testing and evaluation services expenses with TCP. The Company's outstanding obligations to TCP for cytopathology testing services were $604,000 and $308,000 as of December 31, 2018 and 2017, respectively, and are included in accounts payable in the Company's balance sheets. TCP reimburses the Company for TCP's proportionate share of the Company's rent and related operating expenses for the leased facility. TCP's portion of rent and related operating expenses for the shared space at the Austin, Texas facility was $128,000, $114,000 and $103,000 for the years ended December 31, 2018, 2017 and 2016 and is included other income, net in the Company's statements of operations and comprehensive loss.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

Income Taxes (to be updated)

The Company generated a pretax loss of $23.0 million, $31.0 million and $31.4 million in the United States for the years ended December 31, 2018, 2017 and 2016, respectively. Since inception, the Company has not generated any pretax income or loss outside of the United States. The Company recorded no provision for income taxes during the years ended December 31, 2018, 2017 or 2016.

The Company follows FASB ASC No. 740, Income Taxes for the Computation and Presentation of its Tax Provision. The following table presents a reconciliation of the income tax expense computed at the statutory federal rate and the Company's income tax expense for the periods presented (in thousands of dollars):



	Year Ended December, 31,
	2018			2017			2016
U.S. federal taxes at statutory rate	$	(4,825	)	$	(10,541	)	$	(10,662	)
State tax (net of federal benefit)	—			15			20
Non deductible officers's compensation	409			—			—
Permanent differences	285			198			153
Incentive stock options	(256		)	994			1,095
Tax credits	(777		)	(588		)	(677		)
Change in valuation allowance	5,164			(14,552		)	10,071
Rate differential impact - Tax Cuts and Jobs Act	—			24,474			—
Total	$	—		$	—		$	—

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company's deferred tax assets and liabilities are as follows (in thousands of dollars):



	Year Ended December 31,
	2018			2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	50,410		$	47,177		$	61,674
Research and development credits	4,584			4,034			3,174
Stock-based compensation	1,032			2,068			2,847
Accruals, deferred rent and other	2,918			2,375			4,511
Gross deferred tax assets	58,944			55,654			72,206
Valuation allowance	(55,366		)	(51,657		)	(65,975		)
Net deferred tax assets	3,578			3,997			6,231
Deferred tax liabilities:
Property and equipment	(695		)	(983		)	(1,180		)
In-process research and development	(2,883		)	(3,014		)	(5,051		)
Gross deferred tax liabilities	(3,578		)	(3,997		)	(6,231		)
Net deferred tax liabilities	(3,578		)	(3,997		)	(6,231		)
Net deferred taxes	$	—		$	—		$	—

On December 22, 2017, the Tax Cuts and Jobs Act ("The Act") was signed into law. Among other changes is a permanent reduction in the statutory federal corporate income tax rate from 35% to 21% effective January 1, 2018. As a result of the reduction in the corporate income tax rate, the Company revalued its net deferred tax asset at December 31, 2017, to the new statutory rate. This resulted in a reduction in the value of net deferred tax asset of approximately $24.5 million, which was offset by the change in valuation allowance resulting in no impact on the Company's tax expense. The Company has completed the accounting for the income tax effects of the Act, as it relates to its current structure, including provisions that are effective for tax years beginning in 2018. The Company is not expecting these provisions to have a material effect on future results of operations.

The Company has established a full valuation allowance against its net deferred tax assets due to the uncertainty surrounding realization of such assets. The valuation allowance increased $3.7 million during the year ended December 31, 2018, decreased $14.3 million during the year ended December 31, 2017 and increased $10.9 million during the year ended December 31, 2016.

On March 30, 2016, the FASB issued Accounting Standards Update 2016-09, Improvements to Employee Share-Based Accounting, (“ASU 2016-09”). The required adoption period is for financial statements issued for annual periods beginning after December 15, 2016. The Company adopted ASU 2016-09 in the first quarter of 2017 which was applied using a modified retrospective approach. As a result of adoption, the Company’s federal and state net operating losses have been adjusted by excess tax benefits of $1.6 million. Due to a full valuation allowance on all deferred tax assets, there is no impact to the statement of financial position.

As of December 31, 2018, the Company had net operating loss carryforwards of approximately $210.7 million, $56.1 million and $36.6 million available to reduce future taxable income, if any, for federal, California and other state income tax purposes, respectively. The U.S. federal net operating loss carryforwards will begin to expire in 2026 while for state purposes, the net operating losses began to expire in 2028.

As of December 31, 2018, the Company had net research and development credit carryforwards of approximately $4.1 million and $3.8 million available to reduce future taxable income, if any, for federal and state income tax purposes, respectively. The federal credit carryforwards begin to expire in 2028. California credits have no expiration date. Other state credit carryforwards begin to expire in 2023.

The Internal Revenue Code of 1986, as amended, imposes restrictions on the utilization of net operating losses and tax credits in the event of an "ownership change" of a corporation. Accordingly, a company's ability to use net operating losses and tax credits may be limited as prescribed under Internal Revenue Code Section 382 and 383 ("IRC Section 382"). Events which may cause limitations in the amount of the net operating losses or tax credits that the Company may use in any one year include, but are not limited to, a cumulative ownership change of more than 50% over a three-year period. Utilization of the federal and state net operating losses may be subject to substantial annual limitation due to the ownership change limitations provided by the IRC Section 382 rules and similar state provisions. In the event the Company has any changes in ownership, net operating losses and research and development credit carryovers could be limited and may expire unutilized.

Uncertain Tax Positions

As of December 31, 2018, the Company had unrecognized tax benefits of $2.8 million, none of which would currently affect the Company's effective tax rate if recognized due to the Company's deferred tax assets being fully offset by a valuation allowance. The Company does not anticipate that the amount of unrecognized tax benefits relating to tax positions existing at December 31, 2018 will significantly increase or decrease within the next 12 months.

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands of dollars):



	Year Ended December 31,
	2018			2017		2016
Unrecognized tax benefits, beginning of period	$	2,523		$	2,222	$	1,871
Gross increases—tax position in prior period	—			—		—
Gross decreases—tax position in prior period	(97		)	—		—
Gross increases—current period tax position	373			301		351
Lapse of statute of limitations	—			—		—
Unrecognized tax benefits, end of period	$	2,799		$	2,523	$	2,222

It is the Company's policy to include penalties and interest expense related to income taxes as a component of other income (expense), net, and interest expense, respectively, as necessary. There was no interest expense or penalties related to unrecognized tax benefits recorded through December 31, 2018.

The Company's major tax jurisdictions are the United States and California. All of the Company's tax years will remain open for examination by the Federal and state tax authorities for three and four years, respectively, from the date of utilization of the net operating loss or research and development credit. The Company does not have any tax audits pending.

401(k) Plan	12 Months Ended
401(k) Plan	Dec. 31, 2018
Retirement Benefits [Abstract]
401(k) Plan	401(k) Plan The Company sponsors a 401(k) defined contribution plan covering all employees. Employer contributions to the plan were $448,000, $324,000 and $262,000 for the years ended December 31, 2018, 2017, and 2016, respectively.

Subsequent Event (Unaudited) Subsequent Event (Unaudited)	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Event (Unaudited)	Subsequent Event (Unaudited) In January 2019, the Company prepaid $12.5 million of the principal amount of the Term Loan Advance under the Loan and Security Agreement. This did not trigger a prepayment premium because it was a partial, not full, repayment of the principal amount of the Term Loan Advance.

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

The following table presents selected unaudited financial data for each of the eight quarters in the two-year period ended December 31, 2018. The Company believes this information reflects all recurring adjustments necessary to fairly present this information when read in conjunction with the Company's financial statements and the related notes. Net loss per common share, basic and diluted, for the four quarters of each fiscal year may not sum to the total for the fiscal year because of the different number of shares outstanding during each period. The results of operations for any quarter are not necessarily indicative of the results to be expected for any future period (in thousands of dollars, except for share and per share data):



Quarter Ended	March 31			June 30			September 30			December 31
2018:
Revenue	$	20,041		$	22,751		$	23,466		$	25,750
Net loss	(9,177		)	(6,248		)	(4,469		)	(3,105		)
Net loss per common share, basic and diluted	(0.27		)	(0.18		)	(0.12		)	(0.08		)
Shares used to compute net loss per common share, basic and diluted	34,271,254			34,314,234			38,620,036			40,731,334
2017:
Revenue	$	16,432		$	18,406		$	17,519		$	19,596
Net loss	(8,217		)	(7,298		)	(7,049		)	(8,439		)
Net loss per common share, basic and diluted	(0.24		)	(0.22		)	(0.21		)	(0.24		)
Shares used to compute net loss per common share, basic and diluted	33,823,889			33,873,128			33,946,748			35,055,524

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company's financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("U.S. GAAP").
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant items subject to such estimates include: revenue recognition; the useful lives of property and equipment; the recoverability of long-lived assets; the estimation of the fair value of intangible assets; stock options; income tax uncertainties, including a valuation allowance for deferred tax assets; and contingencies. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. These estimates form the basis for making judgments about the carrying values of assets and liabilities and recorded revenue and expenses that are not readily apparent from other sources. Actual results could differ from those estimates and assumptions.
Concentrations of Credit Risk and Other Risks and Uncertainties	Concentrations of Credit Risk and Other Risks and Uncertainties The majority of the Company's cash and cash equivalents are deposited with one major financial institution in the United States. Deposits in this institution may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents. Several of the components of the Company's sample collection kit and test reagents are obtained from single-source suppliers. If these single-source suppliers fail to satisfy the Company's requirements on a timely basis, it could suffer delays in being able to deliver its diagnostic solutions, a possible loss of revenue, or incur higher costs, any of which could adversely affect its operating results. The Company is also subject to credit risk from its accounts receivable related to its sales. The Company does not perform evaluations of customers' financial condition and does not require collateral.
Cash Equivalents	Cash Equivalents Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase. Cash equivalents consist of amounts invested in a money market account primarily consisting of U.S. Treasury reserves.
Restricted Cash	Restricted Cash The Company had deposits of $603,000 included in long-term assets as of December 31, 2018 and December 31, 2017, restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit held as security for the lease of the Company's South San Francisco facility. The Company adopted the FASB issued Accounting Standards Update ("ASU") No. 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash retrospectively as of January 1, 2018 and restricted cash and restricted cash equivalents are included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The adoption of this ASU did not have a material impact on the Company's financial statements.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally between three and five years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the term of the lease. Maintenance and repairs are charged to expense as incurred, and improvements and betterments are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in the statements of operations and comprehensive loss in the period realized.
Finite-lived Intangible Assets	Finite-lived Intangible Assets Finite-lived intangible assets consist of intangible assets reclassified from indefinite-lived intangible assets, following the launch of Percepta in April 2015. The Company amortizes finite-lived intangible assets using the straight-line method over their estimated useful life. The estimated useful life of 15 years was used for the intangible asset related to the Percepta test based on management's estimate of product life, product life of other diagnostic tests and patent life. The Company tests this finite-lived intangible asset for impairment when events or circumstances indicate a reduction in the fair value below its carrying amount. There was no impairment for the years ended December 31, 2018, 2017 or 2016.
Goodwill	Goodwill Goodwill, derived from the Company's acquisition of Allegro Diagnostics Corp. in September 2014, is reviewed for impairment on an annual basis or more frequently if events or circumstances indicate that it may be impaired. The Company's goodwill evaluation is based on both qualitative and quantitative assessments regarding the fair value of goodwill relative to its carrying value. The Company has determined that it operates in a single segment and has a single reporting unit associated with the development and commercialization of diagnostic products. In the event the Company determines that it is more likely than not the carrying value of the reporting unit is higher than its fair value, quantitative testing is performed comparing recorded values to estimated fair values. If impairment is present, the impairment loss is measured as the excess of the recorded goodwill over its implied fair value. The Company performs its annual evaluation of goodwill during the fourth quarter of each fiscal year. There was no impairment for the years ended December 31, 2018, 2017 or 2016.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of certain financial instruments including cash and cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.
Revenue Recognition and Cost of Revenue	As noted above, on July 1, 2016 the Company began recognizing revenue from substantially all its tests on the accrual basis of accounting at an amount equal to management’s best estimate of the cash to ultimately be collected. For tests delivered prior to July 1, 2016, substantially all the related cash had been collected by December 31, 2017. Thus, at January 1, 2018, the cumulative impact of adopting ASC 606 was not material and no adjustment was recorded. Since the Company commenced recognizing revenue from substantially all of its tests on the accrual basis of accounting commencing on July 1, 2016, and continued to do so after the adoption of ASC 606, the adoption of ASC 606 did not have a material impact on the Company's statement of operations for the year ended December 31, 2018. During 2018, the Company changed its revenue estimates due to actual and anticipated cash collections for tests delivered in 2018 or prior quarters and recognized additional revenue of $2.0 million, of which $1.5 million had been collected as of December 31, 2018. This resulted in a decrease in the Company's loss from operations of $2.0 million and a decrease in loss per share of $0.05 for the year ended December 31, 2018. Arrangements with multiple-performance obligations From time to time, the Company enters into arrangements for the research and development and/or commercialization of services. Such arrangements may require us to deliver various rights, services and/or samples, including intellectual property rights/licenses, R&D services, and/or commercialization of services. The underlying terms of these arrangements generally provide for consideration to the Company in the form of nonrefundable upfront license fees, development and commercial performance milestone payments, royalty payments and/or profit sharing. In arrangements involving more than one performance obligation, each required performance obligation is evaluated to determine whether it qualifies as a distinct performance obligation based on whether (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available and (ii) the good or service is separately identifiable from other promises in the contract. The consideration under the arrangement is then allocated to each separate distinct performance obligation based on its respective relative stand-alone selling price. The estimated selling price of each deliverable reflects our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis or using an adjusted market assessment approach if selling price on a stand-alone basis is not available. The consideration allocated to each distinct performance obligation is recognized as revenue when control of the related goods or services is transferred. Consideration associated with at-risk substantive performance milestones is recognized as revenue when it is probable that a significant reversal of the cumulative revenue recognized will not occur. Should there be royalties, the Company utilizes the sales and usage-based royalty exception in arrangements that resulted from the license of intellectual property, recognizing revenues generated from royalties or profit sharing as the underlying sales occur. Biopharmaceutical Services On April 9, 2018, the Company entered into an agreement with a biopharmaceutical company whereby the Company agreed to provide certain tissue samples and other services in exchange for agreed-upon fees. During the quarter ended June 30, 2018, the Company recognized $450,000 of revenue upon deliveries of tissue samples and the Company received $500,000 for other services, which was recognized ratably during the quarters ended September 30 and December 31, 2018 as the services were performed. Thereafter, the Company expects to receive approximately $250,000 per quarter as services are performed and may also recognize revenue related to the deliveries of additional tissue samples as long as the agreement is not terminated. The agreement has a one-year term with an automatic renewal of one year and the biopharmaceutical company may terminate the agreement at any time with at least 90 days' notice. The Company evaluated the accounting for this agreement under ASC 606 and concluded that the performance obligations thereunder are the deliveries of tissue samples and performance of services, both of which are distinct. For the year ended December 31, 2018, the Company recognized revenue of $450,000 for the deliveries of tissue samples and $500,000 for performance of services. There was no deferred revenue related to this agreement at December 31, 2018. Collaboration with Johnson & Johnson On December 28 2018, the Company entered into an agreement with Johnson & Johnson Services, Inc. (JJSI) whereby the Company agreed to provide data to JJSI for the development of their products and JJSI would provide samples and data to the Company to advance the development and commercialization of novel diagnostic tests to detect lung cancer. There are also associated milestones and royalties. As of December 31, 2018, there were no performance of obligations under the agreement or consideration paid. The agreement will be accounted for under our policy on arrangements with multiple-performance obligations mentioned in the footnote above. Cost of Revenue The components of our cost of revenue are laboratory expenses, sample collection expenses, compensation expense, license fees and royalties, depreciation and amortization, other expenses such as equipment and laboratory supplies, and allocations of facility and information technology expenses. Costs associated with performing tests are expensed as the test is processed regardless of whether and when revenue is recognized with respect to that test. Revenue Recognition The Company commenced recognizing revenue in accordance with the provisions of ASC 606, Revenue from Contracts with Customers, or ASC 606, starting January 1, 2018. Prior to January 1, 2018, the Company recognized revenue in accordance with the provisions of ASC 954-605, Health Care Entities - Revenue Recognition, or ASC 954. Revenue from Diagnostic Services Most of the Company’s revenue is generated from the provision of diagnostic services. These services are completed upon the delivery of test results to the prescribing physician, at which time the Company bills for the services. The Company recognizes revenue related to billings based on estimates of the amount that will ultimately be realized. In determining the amount to accrue for a delivered test, the Company considers factors such as payment history, payer coverage, whether there is a reimbursement contract between the payer and the Company, payment as a percentage of agreed upon rate (if applicable), amount paid per test and any current developments or changes that could impact reimbursement. These estimates require significant judgment by management. The Company adopted ASC 606 on January 1, 2018 using the modified retrospective method, which requires a cumulative catch-up adjustment as if the Company had recognized revenue under ASC 606 from January 1, 2016. Prior to January 1, 2018, the Company recognized revenue in accordance with ASC 954 and recognized revenue for tests delivered on an accrual basis when amounts that will ultimately be realized could be reasonably estimated, and on the cash basis when there was insufficient information to estimate revenue accruals. There was sufficient payment history for the Company to substantially accrue all revenue upon delivery of test results starting July 1, 2016 and the Company continued to recognize revenue in 2017 upon cash receipt for unaccrued tests that were delivered prior to July 1, 2016.
Research and Development	Research and Development Research and development expenses include expenses incurred to develop our technology, collect clinical samples and conduct clinical studies to develop and support our products. These expenses consist of compensation expenses, direct research and development expenses such as prototype materials, laboratory supplies and costs associated with setting up and conducting clinical studies at domestic and international sites, professional fees, depreciation and amortization, other miscellaneous expenses and allocation of facility and information technology expenses. We expense all research and development costs in the periods in which they are incurred.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. The Company's assessment of an uncertain tax position begins with the initial determination of the position's sustainability and is measured at the largest amount of benefit that is more-likely-than-not of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit may change as new information becomes available.
Stock-based Compensation	Stock-based Compensation Stock-based compensation expense for equity instruments issued to employees is measured based on the grant-date fair value of the awards. The fair value of each employee stock option is estimated on the date of grant using the Black-Scholes option-pricing model. The Company recognizes compensation costs on a straight-line basis for all employee stock-based compensation awards that are expected to vest over the requisite service period of the awards, which is generally the awards' vesting period. Forfeitures are required to be estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Following the adoption of ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share Based Payment Accounting by the Company on October 1, 2018, stock-based compensation expense for equity instruments issued to non-employees is also measured based on the grant-date fair value of the awards using the Black-Scholes option-pricing model. Prior to this, the fair value of such awards was subject to re-measurement as the underlying equity awards vest.
Net Loss per Common Share	Net Loss per Common Share Basic net loss per common share is calculated by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury stock method. Potentially dilutive securities consisting of options to purchase common stock, restricted stock units and shares subject to purchase under our employee stock purchase plan are considered to be common stock equivalents and were excluded from the calculation of diluted net loss per common share because their effect would be anti-dilutive for all periods presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-2, Leases (Topic 842). This ASU is aimed at making leasing activities more transparent and comparable, and requires substantially all leases be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. The ASU will be effective for interim and annual periods beginning after December 15, 2018. Additionally, the FASB issued ASU, No. 2018-11, Leases (Topic 842): Targeted Improvements, which offers an additional transition method whereby entities may apply the new leases standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings rather than application of the new leases standard at the beginning of the earliest period presented in the financial statements. The Company adopted this standard on January 1, 2019 and has performed an analysis on the impact of this standard and does not expect that this standard will have a material impact on its results of operations or cash flows, but that it will have a material impact on the Company’s assets and liabilities. In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share Based Payment Accounting. Under this ASU, the accounting for share-based payments to nonemployees and employees will be substantially aligned, primarily by permitting the measurement of nonemployee awards to be fixed at the grant date. This ASU is effective for all interim and annual reporting periods beginning on or after December 15, 2018, with early adoption permitted. The Company adopted this ASU on October 1, 2018 using the modified retrospective method. The adoption of the ASU did not result in a cumulative-effect adjustment or have a material impact on the Company's financial position or results of operations. In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808). Under this ASU, transactions in collaborative arrangements are to be accounted for under ASC 606 if the counterparty is a customer for a good or service (or bundle of goods and services) that is a distinct unit of account. Also, entities are precluded from presenting consideration from transactions with a counterparty that is not a customer together with revenue recognized from ASC 606. This ASU is effective for all interim and annual reporting periods beginning on or after December 15, 2019, with early adoption permitted. The Company is currently evaluating the potential effect of this standard on its financial statements.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Revenues [Abstract]

Schedule of Revenue recognized when cash is received and on an accrual basis

Revenue recognized for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands of dollars):



	Year Ended December 31,
	2018				2017				2016
Revenue recognized on the accrual basis	$	92,008	100	%	$	69,274	96	%	$	47,099	72	%
Revenue recognized on the cash basis	—		—	%	2,679		4	%	17,986		28	%
Total	$	92,008	100	%	$	71,953	100	%	$	65,085	100	%

Revenue concentration risk | Revenue

Concentration Risk

Schedule of the Company's third-party payers as a percentage of total

The Company's third-party payers in excess of 10% of revenue and their related revenue as a percentage of total revenue were as follows:



	Year Ended December 31,
	2018		2017		2016
Medicare	29	%	26	%	27	%
UnitedHealthcare	12	%	14	%	12	%
	41	%	40	%	39	%

Gross receivables concentration risk | Accounts receivable

Concentration Risk

Schedule of the Company's third-party payers as a percentage of total

The Company's significant third-party payers in excess of 10% of accounts receivable and their related accounts receivable balance as a percentage of total accounts receivable were as follows:



	As of December 31,
	2018		2017
Medicare	20	%	22	%
UnitedHealthcare	11	%	9	%

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Schedule of outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share



	Year Ended December 31,
	2018	2017	2016
Shares of common stock subject to outstanding options	5,998,163	6,163,734	5,093,454
Employee stock purchase plan	34,869	34,559	36,651
Restricted stock units	384,691	63,425	25,000
Total common stock equivalents	6,417,723	6,261,718	5,155,105

Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2018

Balance Sheet Related Disclosures [Abstract]

Schedule of property and equipment

Property and equipment consisted of the following (in thousands of dollars):



	December 31,
	2018			2017
Leasehold improvements	$	5,825		$	5,790
Laboratory equipment	8,895			8,026
Computer equipment	1,615			1,293
Software, including software developed for internal use	2,450			2,308
Furniture and fixtures	1,435			1,435
Construction-in-process	726			141
Total property and equipment, at cost	20,946			18,993
Accumulated depreciation and amortization	(12,006		)	(9,305		)
Total property and equipment, net	$	8,940		$	9,688

Schedule of accrued liabilities

Accrued liabilities consisted of the following (in thousands of dollars):



	December 31,
	2018		2017
Accrued compensation expense	$	6,412	$	5,293
Accrued other	2,774		2,882
Total accrued liabilities	$	9,186	$	8,175

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of future minimum lease payments under non-cancelable operating leases

Future minimum lease payments under non-cancelable operating leases as of December 31, 2018 are as follows (in thousands of dollars):



Year Ending December 31,	Amounts
2019	$	2,227
2020	2,332
2021	2,401
2022	2,472
2023	2,543
Thereafter	6,840
Total minimum lease payments	$	18,815

Debt (Tables)

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Schedule of net debt obligation

As of December 31, 2018 and 2017, the net debt obligation for borrowings made under the Loan and Security Agreement was as follows (in thousands of dollars):



	December 31,
	2018			2017
Debt principal	$	25,000		$	25,000
End-of-term debt obligation	365			53
Unamortized debt issuance costs	(83		)	(115		)
Net debt obligation	$	25,282		$	24,938

Schedule of future principal payments under the Amended Loan

Future principal and end-of-term debt obligation payments due under the Loan and Security Agreement are as follows (in thousands of dollars):



Year Ending December 31,
2019	$	1,389
2020	8,333
2021	8,333
2022	8,132
Total	$	26,187

Schedule of interest expense on debt

Interest expense was recognized as follows (in thousands of dollars):



	Year Ended December 31,
	2018		2017		2016
Nominal debt interest	$	1,568	$	2,838	$	2,378
Amortization and write-off of debt discount and issuance costs	57		472		173
End-of-term debt obligation interest	312		53		156
Debt prepayment penalty	—		1,536		50
Interest on capital lease	26		42		—
Total	$	1,963	$	4,941	$	2,757

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Schedule of reserved shares of common stock for issuance

As of December 31, 2018 and 2017, the Company had reserved shares of common stock for issuance as follows:



	December 31,
	2018	2017
Stock options and restricted stock units issued and outstanding	6,235,258	6,061,081
Stock options and restricted stock units available for grant under stock option plans	1,571,658	1,133,907
Common stock available for the Employee Stock Purchase Plan	309,419	456,002
Total	8,116,335	7,650,990

Stock Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2018

Stock incentive plans

Summary of activity under the Company's stock option plans

The following table summarizes activity under the Company's stock incentive plans (aggregate intrinsic value in thousands):



	Shares Available for Grant		Stock Options Outstanding and Unvested Stock Units		Weighted Average Exercise Price of Stock Options		Weighted Average Remaining Contractual Life of Stock Options (Years)	Aggregate Intrinsic Value of Stock Options
Balance—December 31, 2017	1,133,907		6,061,081		$	7.76	6.71	$	4,531
Additional shares authorized	1,368,159		—
Granted - stock options	(1,126,750	)	1,126,750		7.08
Granted - restricted stock units	(590,420	)	590,420
Canceled	779,982		(779,982	)	8.00
Exercised	—		(740,010	)	4.71
Restricted stock units vested	—		(23,001	)
Tax portion of restricted stock units vested	6,780		—
Balance—December 31, 2018	1,571,658		6,235,258		$	7.95	6.95	$	27,340

Options vested and exercisable—December 31, 2018			3,341,576		$	8.22	5.87	$	15,829
Options vested and expected to vest—December 31, 2018			5,406,347		$	7.96	6.87	$	26,238

Stock-based Compensation

Stock incentive plans

Summary of share-based compensation expense



	Year Ended December 31,
	2018		2017		2016
Cost of revenue	$	130	$	133	$	126
Research and development	1,018		1,495		1,322
Selling and marketing	1,866		1,899		1,594
General and administrative	2,944		3,090		3,336
Total stock-based compensation expense	$	5,958	$	6,617	$	6,378

Stock-based Compensation, employees

Stock incentive plans

Schedule of assumptions used to calculate estimated grant date fair value of stock options using the Black-Scholes option-pricing valuation model

The estimated grant-date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Weighted-average volatility	50.40 - 52.70%	50.40 - 52.40%	52.49 - 56.36%
Weighted-average expected term (years)	5.50 - 6.08	5.50 - 6.08	5.50 - 6.27
Risk-free interest rate	2.40 - 3.10%	1.80 - 2.33%	1.16 - 2.09%
Expected dividend yield	—	—	—

Stock-based Compensation, non-employees

Stock incentive plans

Schedule of assumptions used to calculate estimated grant date fair value of stock options using the Black-Scholes option-pricing valuation model

The estimated fair value of non-employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Weighted-average volatility	43.60 - 50.50%	50.40 - 51.10%	52.77 - 65.85%
Weighted-average expected term (years)	0.25 - 6.75	6.80 - 7.75	7.80 - 8.56
Risk-free interest rate	1.84 - 2.87%	2.16 - 2.37%	1.39 - 2.30%
Expected dividend yield	—	—	—

Employee stock purchase plan

Stock incentive plans

Schedule of assumptions used to calculate estimated grant date fair value of stock options using the Black-Scholes option-pricing valuation model

The estimated grant date fair value of the ESPP shares was calculated using the Black-Scholes option-pricing model, based on the following assumptions:



	Year Ended December 31,
	2018	2017	2016
Weighted-average volatility	42.88 - 47.74%	37.00 - 43.86%	46.38 - 75.72%
Weighted-average expected term (years)	0.50 - 1.00	0.50 - 1.00	0.50 - 1.00
Risk-free interest rate	1.64 - 2.45%	0.65 - 1.22%	0.40 - 0.50%
Expected dividend yield	—	—	—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of reconciliation of tax expense computed at the statutory federal rate and the Company's tax expense

The following table presents a reconciliation of the income tax expense computed at the statutory federal rate and the Company's income tax expense for the periods presented (in thousands of dollars):



	Year Ended December, 31,
	2018			2017			2016
U.S. federal taxes at statutory rate	$	(4,825	)	$	(10,541	)	$	(10,662	)
State tax (net of federal benefit)	—			15			20
Non deductible officers's compensation	409			—			—
Permanent differences	285			198			153
Incentive stock options	(256		)	994			1,095
Tax credits	(777		)	(588		)	(677		)
Change in valuation allowance	5,164			(14,552		)	10,071
Rate differential impact - Tax Cuts and Jobs Act	—			24,474			—
Total	$	—		$	—		$	—

Schedule of significant components of the Company's deferred tax assets and liabilities

Significant components of the Company's deferred tax assets and liabilities are as follows (in thousands of dollars):



	Year Ended December 31,
	2018			2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	50,410		$	47,177		$	61,674
Research and development credits	4,584			4,034			3,174
Stock-based compensation	1,032			2,068			2,847
Accruals, deferred rent and other	2,918			2,375			4,511
Gross deferred tax assets	58,944			55,654			72,206
Valuation allowance	(55,366		)	(51,657		)	(65,975		)
Net deferred tax assets	3,578			3,997			6,231
Deferred tax liabilities:
Property and equipment	(695		)	(983		)	(1,180		)
In-process research and development	(2,883		)	(3,014		)	(5,051		)
Gross deferred tax liabilities	(3,578		)	(3,997		)	(6,231		)
Net deferred tax liabilities	(3,578		)	(3,997		)	(6,231		)
Net deferred taxes	$	—		$	—		$	—

Schedule of reconciliation of the beginning and ending amount of unrecognized tax benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands of dollars):



	Year Ended December 31,
	2018			2017		2016
Unrecognized tax benefits, beginning of period	$	2,523		$	2,222	$	1,871
Gross increases—tax position in prior period	—			—		—
Gross decreases—tax position in prior period	(97		)	—		—
Gross increases—current period tax position	373			301		351
Lapse of statute of limitations	—			—		—
Unrecognized tax benefits, end of period	$	2,799		$	2,523	$	2,222

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Schedule of selected quarterly financial data (unaudited)

The results of operations for any quarter are not necessarily indicative of the results to be expected for any future period (in thousands of dollars, except for share and per share data):



Quarter Ended	March 31			June 30			September 30			December 31
2018:
Revenue	$	20,041		$	22,751		$	23,466		$	25,750
Net loss	(9,177		)	(6,248		)	(4,469		)	(3,105		)
Net loss per common share, basic and diluted	(0.27		)	(0.18		)	(0.12		)	(0.08		)
Shares used to compute net loss per common share, basic and diluted	34,271,254			34,314,234			38,620,036			40,731,334
2017:
Revenue	$	16,432		$	18,406		$	17,519		$	19,596
Net loss	(8,217		)	(7,298		)	(7,049		)	(8,439		)
Net loss per common share, basic and diluted	(0.24		)	(0.22		)	(0.21		)	(0.24		)
Shares used to compute net loss per common share, basic and diluted	33,823,889			33,873,128			33,946,748			35,055,524

Organization and Description of Business (Details)	12 Months Ended
Organization and Description of Business (Details)	Dec. 31, 2018 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments (in segments)	1

Summary of Significant Accounting Policies - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Jul. 31, 2018	Nov. 30, 2017	Nov. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liquidity
Accumulated deficit				$ 234,086	$ 211,087
Cash and cash equivalents				$ 77,995	$ 33,891	$ 59,219
Number of shares issued in transaction (in shares)	5,750,000		5,723,300
Revolving credit facility \| Line of credit \| Silicon Valley Bank
Liquidity
Proceeds from long-term lines of credit		$ 25,000
Over-Allotment Option
Liquidity
Number of shares issued in transaction (in shares)	750,000		750,000
Proceeds from issuance of common stock	$ 55,000		$ 32,100
Payments of stock issuance costs	$ 3,900		$ 2,200
Common Stock \| Over-Allotment Option
Liquidity
Shares issued, price per share (in usd per share)	$ 10.25		$ 6.00

Summary of Significant Accounting Policies - Credit Risk, Restricted Cash, and Allowance for Doubtful Accounts (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) financial_institution	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Concentrations of Credit Risk and Other Risks and Uncertainties
Number of major financial institutions with which the company's cash and cash equivalents are deposited (in financial institutions) \| financial_institution	1
Restricted Cash
Long term deposit consisting of letter of credit serving as security for lease	$ 603	$ 603	$ 603
Headquarters and laboratory facilities, South San Francisco, Lease expiring 2016
Restricted Cash
Long term deposit consisting of letter of credit serving as security for lease		$ 603
Headquarters and laboratory facilities, South San Francisco, Lease signed in April 2015
Restricted Cash
Long term deposit consisting of letter of credit serving as security for lease	$ 603
Revenue \| Revenue concentration risk
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	41.00%	40.00%	39.00%
Revenue \| Revenue concentration risk \| Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	29.00%	26.00%	27.00%
Revenue \| Revenue concentration risk \| United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	12.00%	14.00%	12.00%
Accounts receivable \| Gross receivables concentration risk \| Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	20.00%	22.00%
Accounts receivable \| Gross receivables concentration risk \| United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	11.00%	9.00%

Summary of Significant Accounting Policies - Intangible Assets, Bonus Accruals, and Revenue Recognition (Details) - USD ($)		3 Months Ended								12 Months Ended
	Apr. 09, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-lived Intangible Assets
Useful life										15 years
Finite-lived intangible assets, impairment										$ 0	$ 0	$ 0
Goodwill
Goodwill impairment										0	0	0
Revenue Recognition
Revenue recognized on an accrual basis										$ 92,008,000	$ 69,274,000	$ 47,099,000
Revenue recognized on accrual basis, percentage										100.00%	96.00%	72.00%
Revenue recognized on a cash basis										$ 0	$ 2,679,000	$ 17,986,000
Revenue recognized on a cash basis, percentage										0.00%	4.00%	28.00%
Total		$ 25,750,000	$ 23,466,000	$ 22,751,000	$ 20,041,000	$ 19,596,000	$ 17,519,000	$ 18,406,000	$ 16,432,000	$ 92,008,000	$ 71,953,000	$ 65,085,000
Total, percentage										100.00%	100.00%	100.00%
Contract with customer, revenue recognized										$ 0	$ 0	$ 948,000
Income (loss) from operations										$ (22,233,000)	$ (26,538,000)	$ (28,803,000)
Net income (loss) per common share, basic and diluted (in dollars per share)		$ (0.08)	$ (0.12)	$ (0.18)	$ (0.27)	$ (0.24)	$ (0.21)	$ (0.22)	$ (0.24)	$ (0.62)	$ (0.91)	$ (1.09)
Biopharmaceutical Company
Revenue Recognition
Deferred revenue		$ 0								$ 0
ASU 2014-09
Revenue Recognition
Deferred revenue		2,000,000								2,000,000
Contract with customer, revenue recognized										1,500,000
Income (loss) from operations										$ 2,000,000
Net income (loss) per common share, basic and diluted (in dollars per share)										$ 0.05
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Useful lives										3 years
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Useful lives										5 years
Product \| Biopharmaceutical Company
Revenue Recognition
Contract with customer, revenue recognized				$ 450,000
Contract agreement term	1 year
Automatic renewal period of contract agreement	1 year
Service
Revenue Recognition
Revenue, amount of remaining performance obligation				$ 500,000
Service \| Biopharmaceutical Company
Revenue Recognition
Contract with customer, revenue recognized										$ 500,000
Revenue, quarterly amount of remaining performance obligation		$ 250,000								$ 250,000

Net Loss Per Share (Details) - shares	12 Months Ended
Net Loss Per Share (Details) - shares	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options (in shares)	6,417,723	6,261,718	5,155,105
Shares of common stock subject to outstanding options
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options (in shares)	5,998,163	6,163,734	5,093,454
Employee stock purchase plan
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options (in shares)	34,869	34,559	36,651
Restricted stock units
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options (in shares)	384,691	63,425	25,000

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment, Net
Total property and equipment, at cost	$ 20,946	$ 18,993
Accumulated depreciation and amortization	(12,006)	(9,305)
Total property and equipment, net	8,940	9,688
Depreciation and amortization expense	2,900	2,800	$ 2,400
Capital leases, accumulated depreciation	367	135
Capital leases, depreciation expense	232	135
Leasehold improvements
Property and Equipment, Net
Total property and equipment, at cost	5,825	5,790
Laboratory equipment
Property and Equipment, Net
Total property and equipment, at cost	8,895	8,026
Capital leased assets	1,200	1,200
Computer equipment
Property and Equipment, Net
Total property and equipment, at cost	1,615	1,293
Software, including software developed for internal use
Property and Equipment, Net
Total property and equipment, at cost	2,450	2,308
Furniture and fixtures
Property and Equipment, Net
Total property and equipment, at cost	1,435	1,435
Construction-in-process
Property and Equipment, Net
Total property and equipment, at cost	$ 726	$ 141

Balance Sheet Components - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance Sheet Related Disclosures [Abstract]
Useful life	15 years
Intangible asset amortization	$ 1.1	$ 1.1	$ 1.1
Accumulated amortization	4.0	$ 3.0	$ 1.9
Annual amortization expense expected to be recognized annually	$ 1.1

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities
Accrued compensation expense	$ 6,412	$ 5,293
Accrued other	2,774	2,882
Total accrued liabilities	$ 9,186	$ 8,175

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Headquarters and laboratory facilities, South San Francisco, Lease signed in April 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Security deposit	$ 603	$ 603
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 76,600	$ 33,100

Commitments and Contingencies - Operating Lease (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Future minimum lease payments under non-cancelable operating leases
2019	$ 2,227
2020	2,332
2021	2,401
2022	2,472
2023	2,543
Thereafter	6,840
Total minimum lease payments	18,815
Facilities rent expense	1,900	$ 1,900	$ 2,000
Supplies Purchase Commitments
Non-cancelable purchase commitment	$ 7,300
Headquarters and laboratory facilities, South San Francisco, Lease signed in April 2015
Operating Leases
Amount of space leased (in square feet) \| ft²	59
Security deposit	$ 603	603
Laboratory facilities, Austin, Texas
Operating Leases
Security deposit	$ 139	$ 139

Commitments and Contingencies - Capital Lease (Details) - Equipment - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Capital Leased Assets [Line Items]
Capital leased assets	$ 1,200	$ 1,200
Capital lease, upfront payment		330
Capital leases, future minimum payments, present value of net minimum payments		$ 874
Annual future minimum lease payment	$ 317

Debt - Loan and Security Agreement (Details) - USD ($)	Nov. 03, 2017	Dec. 31, 2018
Line of Credit Facility [Line Items]
Unamortized debt issuance costs		$ 32,000
Line of credit \| Silicon Valley Bank
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 35,000,000.0
Minimum requirement liability		$ 40,000,000.0
Line of credit \| Silicon Valley Bank \| Secured Debt
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	25,000,000.0
Periodic payment terms, balloon payment to be paid	1,200,000.0
Line of credit \| Silicon Valley Bank \| Revolving credit facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 10,000,000.0
Effective interest rate		8.31%
LIBOR \| Line of credit \| Silicon Valley Bank \| Secured Debt
Line of Credit Facility [Line Items]
Basis spread on variable rate	4.20%
LIBOR \| Line of credit \| Silicon Valley Bank \| Revolving credit facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.50%
Minimum \| LIBOR \| Line of credit \| Silicon Valley Bank \| Secured Debt
Line of Credit Facility [Line Items]
Interest rate, stated percentage	5.43%
Minimum \| LIBOR \| Line of credit \| Silicon Valley Bank \| Revolving credit facility
Line of Credit Facility [Line Items]
Interest rate, stated percentage	4.70%
Debt prepayment tranche one \| LIBOR \| Line of credit \| Silicon Valley Bank \| Revolving credit facility
Line of Credit Facility [Line Items]
Prepayment premium		$ 750,000
Debt prepayment tranche two \| LIBOR \| Line of credit \| Silicon Valley Bank \| Revolving credit facility
Line of Credit Facility [Line Items]
Prepayment premium		500,000
Debt prepayment tranche three \| LIBOR \| Line of credit \| Silicon Valley Bank \| Revolving credit facility
Line of Credit Facility [Line Items]
Prepayment premium		$ 250,000

Debt - Schedule of Loan and Security Agreement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
End-of-term debt obligation	$ 312	$ 53	$ 156
Line of credit
Debt Instrument [Line Items]
Debt principal	25,000	25,000
End-of-term debt obligation	365	53
Unamortized debt issuance costs	(83)	(115)
Net debt obligation	25,282	$ 24,938
2019	1,389
2020	8,333
2021	8,333
2022	8,132
Total	$ 26,187

Debt - Credit Agreement (Details)			3 Months Ended		12 Months Ended
Debt - Credit Agreement (Details)	Nov. 03, 2017 USD ($)	Mar. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2018 USD ($) term_loan installment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Repayments of long-term debt					$ 0	$ 25,385,000	$ 5,000,000
Conversion of accrued interest to long-term debt					0	0	385,000
Prepayment premium					$ 0	$ 1,536,000	$ 288,000
Visium \| Line of credit
Debt Instrument [Line Items]
Number of term loans (in term loans) \| term_loan					2
Line of credit facility, maximum borrowing capacity					$ 40,000,000.0
Repayments of long-term debt	$ 27,300,000
Interest rate, stated percentage					12.00%
Number of installments (in installments) \| installment					8
Term of debt with equal quarterly installments					2 years
Prepayment premium					0.240
Fixed rate percentage paid in cash					0.09
Interest paid-in-kind percentage					0.030
Conversion of accrued interest to long-term debt			$ 385,000	$ 385,000
Prepayment premium	$ 1,500,000
Visium \| Line of credit \| Initial Term Loan
Debt Instrument [Line Items]
Proceeds from lines of credit		$ 25,000,000
Repayments of long-term debt		$ 5,000,000

Debt - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Debt - Interest Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Nominal debt interest	$ 1,568	$ 2,838	$ 2,378
Amortization and write-off of debt discount and issuance costs	57	472	173
End-of-term debt obligation interest	312	53	156
Debt prepayment penalty	0	1,536	50
Interest on capital lease	26	42	0
Total	$ 1,963	$ 4,941	$ 2,757

Stockholders' Equity (Details)	1 Months Ended		12 Months Ended
Stockholders' Equity (Details)	Jul. 31, 2018 USD ($) $ / shares shares	Nov. 30, 2016 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) vote $ / shares shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 USD ($)
Common Stock
Common stock, shares authorized (in shares)			125,000,000	125,000,000
Par value of shares of common stock (in dollars per share) \| $ / shares			$ 0.001	$ 0.001
Number of votes for each share of stock (in votes) \| vote			1
Dividends declared \| $			$ 0
Options issued and outstanding (in shares)			6,235,258	6,061,081
Shares available for issuance (in shares)			1,571,658	1,133,907
Total number of shares reserved for issuance			8,116,335	7,650,990
Number of shares issued in transaction (in shares)	5,750,000	5,723,300
Over-Allotment Option
Common Stock
Proceeds from issuance of common stock \| $	$ 55,000,000	$ 32,100,000
Payments of stock issuance costs \| $	$ 3,900,000	$ 2,200,000
Number of shares issued in transaction (in shares)	750,000	750,000
Shares of common stock subject to outstanding options
Common Stock
Options issued and outstanding (in shares)			6,235,258	6,061,081
Shares available for issuance (in shares)			1,571,658	1,133,907
Employee stock purchase plan
Common Stock
Shares available for issuance (in shares)			309,419	456,002
Common Stock \| Over-Allotment Option
Common Stock
Shares issued, price per share (in usd per share) \| $ / shares	$ 10.25	$ 6.00
Prepaid expenses and other current assets \| Over-Allotment Option
Common Stock
Accounts receivable \| $					$ 200,000

Stock Incentive Plans - Stock Option Plans (Details) - shares	1 Months Ended	12 Months Ended
	Feb. 29, 2008	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2013
Stock incentive plans
Number of shares available for issuance (in shares)		1,571,658	1,133,907
2008 Plan \| ISO \| Minimum
Stock incentive plans
Voting power of person owning stock	10.00%
Option price as a percentage of estimated fair value of shares on date of grant to a person owning stock representing more than 10% of voting power of all classes of stock	110.00%
2008 Plan \| ISO \| Maximum
Stock incentive plans
Term of options granted to a person owning stock representing more than 10% of voting power of all classes of stock	5 years
2008 Plan \| Employee stock options \| Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value	100.00%
2008 Plan \| Employee stock options \| Maximum
Stock incentive plans
Term of options granted	10 years
Stock Incentive Plan 2013
Stock incentive plans
Number of additional shares reserved for issuance (in shares)				1,700,000
Maximum annual increase in outstanding shares on the last day of the immediately preceding fiscal year (as a percent)		4.00%
Number of shares available for issuance (in shares)		1,571,658
Stock Incentive Plan 2013 \| ISO \| Maximum
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
Stock Incentive Plan 2013 \| NSO \| Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
Stock Incentive Plan 2013 \| NSO \| Outside director who was not previously an employee
Stock incentive plans
Percentage of award vesting after one year		25.00%
Shares granted as initial grant (in shares)		35,000
Stock Incentive Plan 2013 \| Employee stock options \| Outside director serving as a member of Board of Directors for at least six months
Stock incentive plans
Shares granted as annual grant (in shares)		10,000
Stock Incentive Plan 2013 \| Employee stock options \| Outside director serving as a member of Board of Directors for at least six months \| Minimum
Stock incentive plans
Period for which director has to serve as board of director to receive grant to purchase shares		6 months
Stock Incentive Plan 2013 \| Employee stock options \| Outside director
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
Stock Incentive Plan 2013 \| Employee stock options \| Outside director \| Maximum
Stock incentive plans
Expiration period after termination of service		12 months
Share-based compensation award, tranche one \| Stock Incentive Plan 2013 \| ISO
Stock incentive plans
Vesting rights, percentage		33.00%
Share-based compensation award, tranche two \| Stock Incentive Plan 2013 \| ISO
Stock incentive plans
Vesting rights, percentage		33.00%
Share-based compensation award, tranche three \| Stock Incentive Plan 2013 \| ISO
Stock incentive plans
Vesting rights, percentage		33.00%

Stock Incentive Plans - Activity Under Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Shares Available for Grant
Balance at the beginning of the period (in shares)	1,133,907
Additional options authorized (in shares)	1,368,159
Canceled (in shares)	779,982
Balance at the end of the period (in shares)	1,571,658	1,133,907
Stock Options Outstanding
Balance at beginning of the period (in shares)	6,061,081
Canceled (in shares)	(779,982)
Exercised (in shares)	(740,010)
Balance at the end of the period (in shares)	6,235,258	6,061,081
Options vested and exercisable at the end of the period (in shares)	3,341,576
Options vested and expected to vest at the end of the period (in shares)	5,406,347
Weighted Average Exercise Price
Balance at beginning of the period (in dollars per share)	$ 7.76
Canceled (in dollars per share)	8.00
Exercised (in dollars per share)	4.71
Balance at the end of the period (in dollars per share)	7.95	$ 7.76
Options vested and exercisable at the end of the period (in dollars per share)	8.22
Options vested and expected to vest at the end of the period (in dollars per share)	$ 7.96
Weighted Average Remaining Contractual Life
Balance	6 years 11 months 12 days	6 years 8 months 16 days
Options vested and exercisable at the end of the period	5 years 10 months 13 days
Options vested and expected to vest at the end of the period	6 years 10 months 13 days
Aggregate Intrinsic Value
Balance (in dollars)	$ 27,340	$ 4,531
Options vested and exercisable at the end of the period (in dollars)	15,829
Options vested and expected to vest at the end of the period (in dollars)	$ 26,238
Employee stock options
Shares Available for Grant
Granted (in shares)	(1,126,750)
Stock Options Outstanding
Granted (in shares)	1,126,750
Weighted Average Exercise Price
Granted (in dollars per share)	$ 7.08
Restricted stock units
Shares Available for Grant
Granted (in shares)	(590,420)
Tax portion of restricted stock units vested (in shares)	6,780
Stock Options Outstanding
Granted (in shares)	590,420
Vested (in shares)	(23,001)
Aggregate Intrinsic Value
Options vested and expected to vest at the end of the period (in dollars)	$ 184	$ 157

Stock Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock incentive plans
Weighted average fair value of options to purchase common stock granted (in dollars per share)	$ 3.62	$ 4.49	$ 3.35
Intrinsic value of stock options exercised (in dollars)	$ 4,900	$ 700	$ 900
Weighted average grant date fair value (in dollars per share)	$ 6.17	$ 8.93
Intrinsic value of stock options outstanding	$ 26,238
Common Stock
Stock incentive plans
Share price (in dollars per share)	$ 12.58	$ 6.53
Employee stock options
Stock incentive plans
Total estimated grant date fair value of options to purchase common stock vested (in dollars)	$ 4,100	$ 3,100	$ 5,800
Restricted stock units
Stock incentive plans
Intrinsic value of stock options outstanding	$ 184	$ 157

Stock Incentive Plans Stock Incentive Plans - ESPP (Details) - Employee stock purchase plan	12 Months Ended
	Dec. 31, 2018 USD ($)
Stock incentive plans
Maximum offering period	12 months
Purchase period	6 months
Maximum fair market value of shares an employee can purchase per calendar year	$ 25,000
Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value	85.00%

Stock Incentive Plans - Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation
Share-based compensation expense (in dollars)	$ 5,958	$ 6,617	$ 6,378
Cost of revenue
Stock-based compensation
Share-based compensation expense (in dollars)	130	133	126
Research and development
Stock-based compensation
Share-based compensation expense (in dollars)	1,018	1,495	1,322
Selling and marketing
Stock-based compensation
Share-based compensation expense (in dollars)	1,866	1,899	1,594
General and administrative
Stock-based compensation
Share-based compensation expense (in dollars)	2,944	$ 3,090	$ 3,336
Stock-based Compensation
Stock-based compensation
Unrecognized compensation expense (in dollars)	$ 9,100
Period over which unrecognized compensation expense expected to be recognized	2 years 3 months 18 days
Stock-based Compensation, employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average volatility, low end of range (as a percent)	0.00%	50.40%	52.49%
Weighted-average volatility, high end of range (as a percent)	0.00%	52.40%	56.36%
Risk-free interest rate, low end of range (as a percent)	0.00%	1.80%	1.16%
Risk-free interest rate, high end of range (as a percent)	0.00%	2.33%	2.09%
Stock-based Compensation, non-employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average volatility, low end of range (as a percent)	0.00%	50.40%	52.77%
Weighted-average volatility, high end of range (as a percent)	0.00%	51.10%	65.85%
Risk-free interest rate, low end of range (as a percent)	0.00%	2.16%	1.39%
Risk-free interest rate, high end of range (as a percent)	0.00%	2.37%	2.30%
Employee stock purchase plan
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average volatility, low end of range (as a percent)	0.00%	37.00%	46.38%
Weighted-average volatility, high end of range (as a percent)	0.00%	43.86%	75.72%
Risk-free interest rate, low end of range (as a percent)	0.00%	0.65%	0.40%
Risk-free interest rate, high end of range (as a percent)	0.00%	1.22%	0.50%
Minimum \| Stock-based Compensation, employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	0 years	5 years 6 months	5 years 6 months
Minimum \| Stock-based Compensation, non-employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	0 years	6 years 9 months 18 days	7 years 9 months 18 days
Minimum \| Employee stock purchase plan
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	0 years	6 months	6 months
Maximum \| Stock-based Compensation, employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	0 years	6 years 29 days	6 years 3 months 7 days
Maximum \| Stock-based Compensation, non-employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	0 years	7 years 9 months	8 years 6 months 22 days
Maximum \| Employee stock purchase plan
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	0 years	1 year	1 year

Genzyme Co-promotion Agreement (Details)	12 Months Ended
Genzyme Co-promotion Agreement (Details)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 28, 2015 country_	Jan. 31, 2012 USD ($) country_
Genzyme Co-promotion Agreement
Amortization of up-front co-promotion fee	$ 0	$ 0	$ 948,000
Co-promotion agreement \| Genzyme
Genzyme Co-promotion Agreement
Co-promotion expenses			6,100,000
Outstanding obligation to Genzyme		$ 0
Amortization of up-front co-promotion fee			$ 900,000
Afirma thyroid diagnostic solution co-promotion agreement \| Genzyme
Genzyme Co-promotion Agreement
Number of countries outside United States for exclusive promotion under the agreement \| country_					40
Deferred revenue					$ 10,000,000
Ex-U.S. Co-Promotion Agreement \| Genzyme
Genzyme Co-promotion Agreement
Number of countries outside United States for exclusive promotion under the agreement \| country_				5

- Details

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Data Type:	na
Balance Type:
Period Type:

Thyroid Cytopathology Partners (Details)	12 Months Ended
Thyroid Cytopathology Partners (Details)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2010 USD ($)	Oct. 16, 2017 USD ($) installment
Thyroid Cytopathology Partners
Outstanding obligations	$ 2,516,000	$ 3,853,000
Thyroid Cytopathology Partners
Thyroid Cytopathology Partners
Direct monetary compensation				$ 0
Notice of intent not to renew period	12 months
Contract termination fee					$ 1,800,000.0
Quarterly installments (in installments) \| installment					8
Expenses for cytopathology testing and evaluation services	$ 3,900,000	4,600,000	$ 5,100,000
Outstanding obligations	604,000	308,000
Reduction to rent expense for TCP's portion of costs for shared space	$ 128,000	$ 114,000	$ 103,000

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Pretax loss	$ 23,000,000	$ 31,000,000	$ 31,400,000
Income tax expense (benefit)	0	0	0
Tax Cuts and Jobs Act of 2017, deferred tax asset decrease		24,500,000
Increase (decrease) in valuation allowance against deferred tax assets	3,700,000	$ (14,300,000)	$ 10,900,000
Share-based compensation excess tax benefit amount	1,600,000
Federal
Operating loss carryforwards
Net operating loss carryforwards	210,700,000
Tax credit carryforward	4,100,000
State
Operating loss carryforwards
Tax credit carryforward	3,800,000
State \| California
Operating loss carryforwards
Net operating loss carryforwards	56,100,000
State \| Other state income tax purposes
Operating loss carryforwards
Net operating loss carryforwards	$ 36,600,000

Income Taxes - Tax Provision (Details) - USD ($)	12 Months Ended
Income Taxes - Tax Provision (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of tax expense computed at the statutory federal rate and the Company's tax expense
U.S. federal taxes at statutory rate	$ (4,825,000)	$ (10,541,000)	$ (10,662,000)
State tax (net of federal benefit)	0	15,000	20,000
Non deductible officers's compensation	409,000	0	0
Permanent differences	285,000	198,000	153,000
Incentive stock options	(256,000)	994,000	1,095,000
Tax credits	(777,000)	(588,000)	(677,000)
Change in valuation allowance	5,164,000	(14,552,000)	10,071,000
Rate differential impact - Tax Cuts and Jobs Act	0	24,474,000	0
Total	$ 0	$ 0	$ 0

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 50,410	$ 47,177	$ 61,674
Research and development credits	4,584	4,034	3,174
Stock-based compensation	1,032	2,068	2,847
Accruals, deferred rent and other	2,918	2,375	4,511
Gross deferred tax assets	58,944	55,654	72,206
Valuation allowance	(55,366)	(51,657)	(65,975)
Net deferred tax assets	3,578	3,997	6,231
Deferred tax liabilities:
Property and equipment	(695)	(983)	(1,180)
In-process research and development	(2,883)	(3,014)	(5,051)
Gross deferred tax liabilities	(3,578)	(3,997)	(6,231)
Net deferred tax liabilities	(3,578)	(3,997)	(6,231)
Net deferred taxes	$ 0	$ 0	$ 0

Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Unrecognized tax benefits, beginning of period	$ 2,523	$ 2,222	$ 1,871
Gross increases—tax position in prior period	0	0	0
Gross decreases—tax position in prior period	(97)	0	0
Gross increases—current period tax position	373	301	351
Lapse of statute of limitations	0	0	0
Unrecognized tax benefits, end of period	2,799	$ 2,523	$ 2,222
Interest expense or penalties related to unrecognized tax benefits	$ 0

Income Taxes - Income Tax Examination (Details)	12 Months Ended
Income Taxes - Income Tax Examination (Details)	Dec. 31, 2018
Federal
Income tax examination
Income tax examination period	3 years
State
Income tax examination
Income tax examination period	4 years

401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
401(k) Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Employer contributions to the plan	$ 448	$ 324	$ 262

Subsequent Event (Unaudited) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Repayments of long-term debt		$ 0	$ 25,385	$ 5,000
Revolving credit facility \| Line of credit \| Silicon Valley Bank \| Subsequent Event
Subsequent Event [Line Items]
Repayments of long-term debt	$ 12,500

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data (Unaudited)
Revenue	$ 25,750	$ 23,466	$ 22,751	$ 20,041	$ 19,596	$ 17,519	$ 18,406	$ 16,432	$ 92,008	$ 71,953	$ 65,085
Net loss	$ (3,105)	$ (4,469)	$ (6,248)	$ (9,177)	$ (8,439)	$ (7,049)	$ (7,298)	$ (8,217)	$ (22,999)	$ (31,003)	$ (31,358)
Net loss per common share, basic and diluted (in dollars per share)	$ (0.08)	$ (0.12)	$ (0.18)	$ (0.27)	$ (0.24)	$ (0.21)	$ (0.22)	$ (0.24)	$ (0.62)	$ (0.91)	$ (1.09)
Shares use to compute net loss per common share, basic and diluted (in shares)	40,731,334	38,620,036	34,314,234	34,271,254	35,055,524	33,946,748	33,873,128	33,823,889	37,020,246	33,925,617	28,830,472