Veracyte (VCYT) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	VERACYTE, INC.
Entity Central Index Key	1,384,101
Document Type	10-K
Document Period End Date	Dec. 31, 2017
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 Public Float			$ 225.6
Entity Common Stock, Shares Outstanding		34,290,774
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 33,891	$ 59,219
Accounts receivable	12,716	8,756
Supplies inventory	5,324	3,475
Prepaid expenses and other current assets	1,997	2,057
Restricted cash	0	120
Total current assets	53,928	73,627
Property and equipment, net	9,688	11,480
Finite-lived intangible assets, net	13,067	14,133
Goodwill	1,057	1,057
Restricted cash	603	603
Other assets	326	134
Total assets	78,669	101,034
Current liabilities:
Accounts payable	3,853	2,424
Accrued liabilities	8,175	9,110
Total current liabilities	12,028	11,534
Long-term debt	24,938	24,918
Capital lease liability, net of current portion	308	599
Deferred rent, net of current portion	4,170	4,402
Total liabilities	41,444	41,453
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, 2017 and 2016	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized, 34,210,388 and 33,762,278 shares issued and outstanding as of December 31, 2017 and 2016, respectively	34	34
Additional paid-in capital	248,278	239,631
Accumulated deficit	(211,087)	(180,084)
Total stockholders' equity	37,225	59,581
Total liabilities and stockholders' equity	$ 78,669	$ 101,034

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
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	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 Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 71,953	$ 65,085	$ 49,503
Operating Expenses:
Cost of revenue	28,195	25,462	21,497
Research and development	13,881	15,324	12,796
Selling and marketing	32,260	28,248	25,293
General and administrative	23,088	23,787	22,583
Intangible asset amortization	1,067	1,067	800
Total operating expenses	98,491	93,888	82,969
Loss from operations	(26,538)	(28,803)	(33,466)
Interest expense	(4,941)	(2,757)	(378)
Other income, net	476	202	140
Net loss	(31,003)	(31,358)	(33,704)
Comprehensive loss	$ (31,003)	$ (31,358)	$ (33,704)
Net loss per common share, basic and diluted (in dollars per share)	$ (0.91)	$ (1.09)	$ (1.30)
Shares use to compute net loss per common share, basic and diluted (in shares)	33,925,617	28,830,472	25,994,193

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2014	$ 41,374	$ 23	$ 156,373	$ (115,022)
Balance (in shares) at Dec. 31, 2014		22,523,529
Increase (Decrease) in Convertible Preferred Stock and Stockholders' Equity (Deficit)
Issuance of common stock on exercise of stock options	722		722
Issuance of common stock on exercise of stock options (in shares)		253,787
Sale of common stock in a private placement, net of issuance costs	37,258	$ 5	37,253
Sale of common stock in a private placement, net of issuance costs (in shares)		4,907,975
Issuance of common stock in a private placement, issuance cost	2,742
Stock-based compensation expense (employee)	5,302		5,302
Stock-based compensation expense (non-employee)	110		110
Stock-based compensation expense (ESPP)	190		190
Net loss	(33,704)			(33,704)
Comprehensive loss	(33,704)			(33,704)
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 Convertible Preferred Stock and Stockholders' Equity (Deficit)
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
Issuance of common stock in a private placement, issuance cost	2,247
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)
Comprehensive loss	(31,358)			(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 Convertible Preferred Stock and Stockholders' Equity (Deficit)
Issuance of common stock on exercise of stock options and vesting of restricted stock units (in shares)		295,059
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 (in shares)	279,454
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)
Comprehensive loss	(31,003)			(31,003)
Balance at Dec. 31, 2017	$ 37,225	$ 34	$ 248,278	$ (211,087)
Balance (in shares) at Dec. 31, 2017		34,210,388

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (31,003)	$ (31,358)	$ (33,704)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,841	3,511	2,254
Bad debt expense	0	68	105
Loss on disposal of property and equipment	12	12	0
Genzyme co-promotion fee amortization	0	(948)	(1,897)
Stock-based compensation	6,617	6,378	5,602
Conversion of accrued interest to long-term debt	0	385	0
Amortization and write-off of debt discount and issuance costs	472	173	46
Interest on end-of-term debt obligation and prepayment penalty	1,589	206	79
Changes in operating assets and liabilities:
Accounts receivable	(3,960)	(5,321)	(558)
Supplies inventory	(1,849)	292	(71)
Prepaid expenses and current other assets	(7)	(415)	304
Other assets	(192)	25	(42)
Accounts payable	1,728	(1,441)	(3,546)
Accrued liabilities and deferred rent	(1,163)	451	4,463
Net cash used in operating activities	(23,915)	(27,982)	(26,965)
Investing activities
Purchases of property and equipment	(1,755)	(4,210)	(6,165)
Proceeds from the sale of property and equipment	440	0	0
Change in restricted cash	120	(2)	(533)
Net cash used in investing activities	(1,195)	(4,212)	(6,698)
Financing activities
Proceeds from the issuance of long-term debt, net of debt issuance costs	24,880	24,452	0
Proceeds from issuance of common stock in a private placement, net of issuance costs	0	0	37,258
Proceeds from issuance of common stock in a public offering, net of issuance costs	200	31,949	0
Payment of long-term debt	(25,385)	(5,000)	0
Payment of end-of-term debt obligation and prepayment penalty	(1,536)	(288)	0
Payment of deferred stock offering costs	0	0	(247)
Payment of capital lease liability	(274)	0	0
Proceeds from the exercise of common stock options and employee stock purchases	1,897	1,216	722
Net cash (used in) provided by financing activities	(218)	52,329	37,733
Net (decrease) increase in cash and cash equivalents	(25,328)	20,135	4,070
Cash and cash equivalents at beginning of year	59,219	39,084	35,014
Cash and cash equivalents at end of year	33,891	59,219	39,084
Supplementary cash flow information of non-cash investing and financing activities:
Net receivable for reimbursement of public offering issuance costs	0	144	0
Purchases of property and equipment included in accounts payable and accrued liabilities	42	363	1,825
Supplementary cash flow information:
Cash paid for interest on debt	2,718	2,149	278
Cash paid for tax	$ 21	$ 7	$ 22

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Veracyte, Inc. (“Veracyte” or the “Company”) 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. Veracyte is a genomic diagnostics company that resolves diagnostic uncertainty by uniquely combining genomic technology, clinical science and machine learning to provide diagnostic answers to physicians and patients. Since the Company's founding in 2008, it has commercialized three products: Afirma Thyroid FNA Analysis - Includes the next-generation Afirma Genomic Sequencing Classifier, or GSC, and its predecessor, the Afirma Gene Expression Classifier, or GEC that is used to identify patients with benign thyroid nodules among those with indeterminate cytopathology results in order to preserve the thyroid. The Afirma classifier was developed using machine learning that is based on ensemble methods in which multiple algorithms - each playing its own role - are used to interpret large amounts of ribonucleic acid ("RNA") sequencing genomic data and obtain a better predictive performance than any single algorithm on its own. Percepta Bronchial Genomic Classifier - The 23-gene Percepta classifier improves lung cancer screening and diagnosis by increasing the diagnostic performance of bronchoscopies and identifying patients with lung nodules who are at low risk of cancer, without the need for more invasive procedures. The test analyzes genomic changes that occur in the epithelial cells lining the airways of current or former smokers to assess a patient’s risk of having lung cancer, without the need to test the often-hard-to-reach nodule directly. Envisia Genomic Classifier - The Envisia classifier is designed to improve physicians’ ability to differentiate idiopathic pulmonary fibrosis, or IPF, from other interstitial lung diseases, or ILD, without the need for invasive and potentially risky surgery. The Envisia classifier uses machine learning coupled with powerful, deep RNA sequencing to detect the presence or absence of usual interstitial pneumonia, or UIP, a classic diagnostic pattern whose presence is essential for the diagnosis of IPF. All of the Company's testing services are made available through its clinical reference laboratories located in South San Francisco, California and Austin, Texas, which are each certified under the Clinical Laboratory Improvement Amendments of 1988, or CLIA.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	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"). The financial statements include the accounts of the Company and its former wholly-owned subsidiary, which was dissolved in June 2015. For periods prior to the subsidiary dissolution, all intercompany accounts and transactions were eliminated in consolidation. 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 2018 and in future years. As of December 31, 2017 , the Company had an accumulated deficit of $211.1 million . The Company may never achieve revenue sufficient to offset its expenses. The Company believes its cash and cash equivalents of $33.9 million as of December 31, 2017 and its revenue from sales in 2018 will be sufficient to meet its anticipated cash requirements through at least March 2019. 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, 2017 , 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, 2017 2016 2015 Medicare 26 % 27 % 26 % UnitedHealthcare 14 % 12 % 14 % 40 % 39 % 40 % 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: December 31, 2017 2016 Medicare 22 % 18 % 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 $120,000 included in current assets as of December 31, 2016 , pledged for corporate cards. There was no such restricted amount as of December 31, 2017 . The Company also had deposits of $603,000 included in long-term assets as of December 31, 2017 and December 31, 2016 , 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. Supplies Inventory Supplies inventory consists of test reagents and other consumables primarily used in the sample collection kits and in cytopathology and genomic classifier test processing, and are valued at the lower of cost or market value. Cost is determined using actual costs on a first-in, first-out basis. 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 consists 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, 2017 , 2016 or 2015 . 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, 2017 , 2016 or 2015 . 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 recognizes revenue in accordance with the provision of ASC 954-605, Health Care Entities—Revenue Recognition ("ASC 954") . The Company's revenue is generated from the provision of diagnostic services. The service is completed upon the delivery of test results to the prescribing physician, at which time the Company bills for the service. The Company recognizes revenue related to billings for tests delivered on an accrual basis when amounts that will ultimately be realized can be reasonably estimated. The estimates of amounts that will ultimately be realized requires significant judgment by management. Until a contract has been negotiated with a commercial payer or governmental program, the Company's tests may or may not be covered by these entities' existing reimbursement policies. In addition, patients do not enter into direct agreements with the Company that commit them to pay any portion of the cost of the tests in the event that their insurance declines to reimburse the Company. The Company may bill the patient directly for these amounts in the form of co-payments and co-insurance in accordance with their insurance carrier and health plans. In the absence of contracted reimbursement or the ability to estimate the amount that will ultimately be realized for the Company's services, revenue is recognized on the cash basis. Revenue recognized for the years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands of dollars): Year Ended December 31, 2017 2016 2015 Revenue recognized on the accrual basis $ 69,274 96 % $ 47,099 72 % $ 27,043 55 % Revenue recognized on the cash basis 2,679 4 % 17,986 28 % 22,460 45 % Total $ 71,953 100 % $ 65,085 100 % $ 49,503 100 % Prior to July 1, 2016, the Company believed it did not have a consistent enough payment history to accrue a significant portion of its Afirma tests delivered to customers and, as noted above, recognized revenue on the cash basis for such tests. The Company has been analyzing the amounts received for tests performed since commercialization and during the quarter ended September 30, 2016, sufficient information developed to support a reasonable estimate of the amount of revenue to accrue upon test delivery for a number of payers that had been previously recognized on the cash basis. In determining the amount to accrue for a particular test, the Company considered factors such as payer coverage, whether there is a reimbursement contract between the payer and the Company, timeliness of payment, payment as a percentage of agreed upon rate (if applicable), amount paid per test and any current developments or changes that could impact reimbursement. As a result, the Company recognized $3.5 million of incremental revenue during the quarter ended September 30, 2016 upon test delivery that previously would not have been recognized until cash was received. Tests performed prior to July 1, 2016 that did not meet the Company’s accrual criteria at the time of delivery will continue to be recognized as revenue on the cash basis. However, the Company expects the amount of revenue to be recognized on the cash basis for Afirma to decline in future periods since subsequent to September 2016 relatively few tests were performed for which a reasonable estimate of revenue to accrue was not made at the time of delivery. 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. Equity awards issued to non-employees are valued using the Black-Scholes option-pricing model and are 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 May 2014, the Financial Accounting Standards Board, or FASB, issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), to supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing U.S. GAAP. The Company will adopt the new revenue standard as of January 1, 2018 using the modified retrospective method. The Company has completed its assessment of the five steps of this ASU and believes that the adoption of this ASU will not result in a material cumulative catch-up adjustment under the modified retrospective method, or have a material impact on the Company's financial position or results of operations. In February 2016, the FASB issued ASU No. 2016-2, Leases . 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. Entities are required to use a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited and early adoption is permitted. The Company is currently evaluating the potential effect of this standard on its financial statements. In March 2016, the FASB issued ASU 2016-9, Compensation - Stock Compensation , related to the tax effects of share-based awards. The ASU requires that all the tax effects of share-based awards be recorded through the income statement, thereby simplifying the current guidance that requires excess tax benefits and certain excess tax deficiencies to be recorded in equity. This ASU also permits an election for the impact of forfeitures on the recognition of expense for share-based payment awards where forfeitures can be estimated or recognized when they occur. This ASU was effective for interim and annual periods beginning after December 15, 2016. The Company adopted this ASU as of January 1, 2017 and elected to continue using its forfeiture estimation method for share-based payment awards. This ASU was adopted prospectively and the impact of adoption on the Company's financial statements was not material. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , provides specific guidance on cash flow classification issues, including classifying debt prepayment or debt extinguishment costs under financing activities in the statements of cash flows. The amendments in ASU 2016-15 are effective for interim and annual periods beginning after December 15, 2017. The ASU should be applied using a retrospective transition method, unless it is impracticable to do so for some of the issues. In such case, the amendments for those issues would be applied prospectively as of the earliest date practicable. Early adoption is permitted. This ASU was adopted retrospectively and the impact of adoption on the Company's financial statements was not material because prior period debt prepayment costs were immaterial and already included under financing activities in the statements of cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash. This ASU requires that restricted cash and restricted cash equivalents be 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 ASU will be effective for interim and annual periods beginning after December 15, 2017. The Company does not anticipate that the adoption of this ASU will have a significant impact on its financial statements.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss Per Share	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, 2017 , 2016 and 2015 because their inclusion would be anti-dilutive: Year Ended December 31, 2017 2016 2015 Shares of common stock subject to outstanding options 6,163,734 5,093,454 4,086,640 Employee stock purchase plan 34,559 36,651 15,561 Restricted stock units 63,425 25,000 — Total common stock equivalents 6,261,718 5,155,105 4,102,201

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment, Net Property and equipment consisted of the following (in thousands of dollars): Year Ended December 31, 2017 2016 Leasehold improvements $ 5,790 $ 5,861 Laboratory equipment 8,026 6,441 Computer equipment 1,293 1,177 Software, including software developed for internal use 2,308 1,937 Furniture and fixtures 1,435 1,131 Construction-in-process 141 1,769 Total property and equipment, at cost 18,993 18,316 Accumulated depreciation and amortization (9,305 ) (6,836 ) Total property and equipment, net $ 9,688 $ 11,480 Depreciation and amortization expense was $2.8 million , $2.4 million and $1.5 million for the years ended December 31, 2017 , 2016 and 2015 , 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 $135,000 at December 31, 2017 , and depreciation of $135,000 for the year ended December 31, 2017 . 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 , $1.1 million , and $0.8 million was recognized for the years ended December 31, 2017 , 2016 , and 2015 , respectively, and accumulated amortization was $3.0 million , $1.9 million , and $0.8 million as of December 31, 2017 , 2016 , and 2015 , 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): Year Ended December 31, 2017 2016 Accrued compensation expense $ 5,293 $ 6,120 Accrued other 2,882 2,990 Total accrued liabilities $ 8,175 $ 9,110

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	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. • 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 include 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 $33.1 million and $58.7 million as of December 31, 2017 and 2016 , 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, 2017 and 2016 , respectively, and are Level I assets as described above.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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, 2017 and 2016 , 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 and $75,000 , which is included in other assets in the Company's balance sheets as of December 31, 2017 and 2016 , respectively. Future minimum lease payments under non-cancelable operating leases as of December 31, 2017 are as follows (in thousands of dollars): Year Ending December 31, Amounts 2018 $ 2,121 2019 2,227 2020 2,332 2021 2,401 2022 2,472 Thereafter 9,384 Total minimum lease payments $ 20,937 The Company recognizes rent expense on a straight-line basis over the non-cancelable lease period. Rent expense was $1.9 million , $2.0 million , and $1.9 million for the years ended December 31, 2017 , 2016 and 2015 , 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 was $874,000 . As at December 31, 2017 , the annual future minimum lease payments will be $317,000 for each of 2018 and 2019. Supplies Purchase Commitments The Company had non-cancelable purchase commitments with suppliers to purchase a minimum quantity of supplies for approximately $7.1 million at December 31, 2017 . 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, individually or in the aggregate, a material impact on the Company's financial statements.

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	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, 2017. 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 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. 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, 2017 , the Company was in compliance with the loan covenants. As of December 31, 2017 , the net debt obligation for borrowings made under the Loan and Security Agreement was as follows (in thousands of dollars): December 31, 2017 Debt principal $ 25,000 End-of-term debt obligation 53 Unamortized debt issuance costs (115 ) Net debt obligation $ 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 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 . As of December 31, 2016 , the net debt obligation for borrowings made under the Loan and Security Agreement was as follows (in thousands of dollars): December 31, 2016 Debt principal $ 25,385 Unamortized debt issuance costs (467 ) Net debt obligation $ 24,918 Interest Expense Interest expense was recognized as follows (in thousands of dollars): Year Ended December 31, 2017 2016 2015 Nominal debt interest $ 2,838 $ 2,378 $ 253 Amortization and write-off of debt discount and issuance costs 472 173 46 End-of-term debt obligation interest 53 156 79 Debt prepayment penalty 1,536 50 — Interest on capital lease 42 — — Total $ 4,941 $ 2,757 $ 378

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	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, 2017 . As of December 31, 2017 and 2016 , the Company had reserved shares of common stock for issuance as follows: December 31, 2017 2016 Stock options and restricted stock units issued and outstanding 6,061,081 5,251,832 Stock options and restricted stock units available for grant under stock option plans 1,133,907 887,724 Common stock available for the Employee Stock Purchase Plan 456,002 609,053 Total 7,650,990 6,748,609 In November 2016, the Company completed a public offering of 5,723,300 shares of its common stock at a price of $6.00 per share. Net proceeds to the Company were $32.1 million , after deducting underwriting discounts and commissions and other 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. In April 2015, the Company completed a private placement of 4,907,975 shares of its common stock to certain accredited investors at a purchase price of $8.15 per share. Net proceeds to the Company were $37.3 million , after deducting placement agent fees and other expenses of $2.7 million .

Stock Incentive Plans

Stock Incentive Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Incentive Plans	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, 2017 , 1,133,907 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 10 th 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 Weighted Weighted Average Aggregate Balance—December 31, 2016 887,724 5,251,832 $ 7.56 7.24 $ 8,515 Additional shares authorized 1,350,491 — Granted - stock options (1,769,000 ) 1,769,000 8.80 Granted - restricted stock units (60,000 ) 60,000 Canceled 715,297 (715,297 ) 9.94 Exercised — (279,454 ) 5.13 Restricted stock units vested — (25,000 ) Tax portion of restricted stock units vested 9,395 — Balance—December 31, 2017 1,133,907 6,061,081 $ 7.76 6.71 $ 4,531 Options vested and exercisable—December 31, 2017 3,174,848 $ 7.43 5.58 $ 4,257 Options vested and expected to vest—December 31, 2017 5,749,963 $ 7.74 6.64 $ 4,509 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 $6.53 and $7.74 per share as of December 31, 2017 and 2016, respectively. The weighted average fair value of options to purchase common stock granted was $4.49 , $3.35 and $5.12 for the years ended December 31, 2017, 2016 and 2015, respectively. The aggregate estimated grant date fair value of employee options to purchase common stock vested during the years ended December 31, 2017, 2016 and 2015 was $3.1 million , $5.8 million and $5.3 million , respectively. The intrinsic value of stock options exercised was $0.7 million , $0.9 million and $1.8 million for the years ended December 31, 2017, 2016 and 2015, respectively. The weighted average fair value of restricted stock units granted was $8.93 and $7.47 for the years ended December 31, 2017 and 2016, respectively. The intrinsic value of restricted stock units vested was $157,000 for the year ended December 31, 2017 for the first stock units issued in December 2016. Employee Stock Purchase Plan In May 2015, the Company's stockholders approved the Company's Employee Stock Purchase Plan ("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, 2017, 2016 and 2015, and are included in the statements of operations and comprehensive loss as follows (in thousands of dollars): Year Ended December 31, 2017 2016 2015 Cost of revenue $ 133 $ 126 $ 100 Research and development 1,495 1,322 1,178 Selling and marketing 1,899 1,594 1,326 General and administrative 3,090 3,336 2,998 Total stock-based compensation expense $ 6,617 $ 6,378 $ 5,602 As of December 31, 2017, the Company had $9.2 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 2.50 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, 2017 2016 2015 Weighted-average volatility 50.40 - 52.40% 52.49 - 56.36% 52.56 - 68.82% Weighted-average expected term (years) 5.50 - 6.08 5.50 - 6.27 5.50 - 6.08 Risk-free interest rate 1.80 - 2.33% 1.16 - 2.09% 1.55 - 2.03% 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, 2017 2016 2015 Weighted-average volatility 50.40 - 51.10% 52.77 - 65.85% 64.72 - 74.48% Weighted-average expected term (years) 6.80 - 7.75 7.80 - 8.56 7.92 - 10.00 Risk-free interest rate 2.16 - 2.37% 1.39 - 2.30% 1.78 - 2.29% 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, 2017 2016 2015 Weighted-average volatility 37.00 - 43.86% 46.38 - 75.72% 53.57 - 58.10% Weighted-average expected term (years) 0.50 - 1.00 0.50 - 1.00 0.49 - 0.99 Risk-free interest rate 0.65 - 1.22% 0.40 - 0.50% 0.17 - 0.33% Expected dividend yield — — —

Genzyme Co-promotion Agreement

Genzyme Co-promotion Agreement	12 Months Ended
	Dec. 31, 2017
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. On March 9, 2016, as permitted under the agreement, the Company gave Genzyme notice of termination effective September 9, 2016 with the remaining portion of the upfront co-promotion fee recognized through that date as well. 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 was to continue until December 31, 2019, with extension of the agreement possible upon agreement of the parties. Pursuant to the agreement, the Company agreed to pay Genzyme 25% of net revenue from the sale of the Afirma solution test in Brazil and Singapore over a five -year period commencing January 1, 2015. These payments were immaterial for all periods presented. Effective July 6, 2017, the agreement was terminated and payments made under this agreement for all periods presented were not material. The Company incurred $6.1 million and $7.3 million in co-promotion expense, excluding the amortization of the upfront co-promotion fee, in the years ended December 31, 2016 and 2015, respectively, 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, 2017 or December 31, 2016 . The Company amortized $0.9 million and $1.9 million of the $10.0 million upfront co-promotion fee in the years ended December 31, 2016 and 2015, respectively, 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

Thyroid Cytopathology Partners	12 Months Ended
	Dec. 31, 2017
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. The Company incurred $4.6 million , $5.1 million , and $4.7 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, in cytopathology testing and evaluation services expenses with TCP. The Company's outstanding obligations to TCP for cytopathology testing services were $308,000 and $426,000 as of December 31, 2017 and 2016 , respectively, and are included in accounts payable in the accompanying 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 $114,000 , $103,000 and $90,000 for the years ended December 31, 2017 , 2016 and 2015 and is included other income, net in the Company's statements of operations and comprehensive loss.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company generated a pretax loss of $31.0 million , $31.4 million and $33.7 million in the United States for the years ended December 31, 2017 , 2016 and 2015 , 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, 2017 , 2016 or 2015 . 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, 2017 2016 2015 U.S. federal taxes at statutory rate $ (10,541 ) $ (10,662 ) $ (11,459 ) State tax (net of federal benefit) 15 20 (30 ) Permanent differences 198 153 96 Incentive stock options 994 1,095 789 Tax credits (588 ) (677 ) (581 ) Change in valuation allowance (14,552 ) 10,071 11,185 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, 2017 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 47,177 $ 61,674 $ 52,262 Research and development credits 4,034 3,174 2,497 Stock-based compensation 2,068 2,847 1,825 Genzyme co-promotion agreement — — 330 Accruals, deferred rent and other 2,375 4,511 4,698 Gross deferred tax assets 55,654 72,206 61,612 Valuation allowance (51,657 ) (65,975 ) (55,101 ) Net deferred tax assets 3,997 6,231 6,511 Deferred tax liabilities: Property and equipment (983 ) (1,180 ) (1,215 ) In-process research and development (3,014 ) (5,051 ) (5,296 ) Gross deferred tax liabilities (3,997 ) (6,231 ) (6,511 ) Net deferred tax liabilities (3,997 ) (6,231 ) (6,511 ) 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 a preliminary assessment of 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's preliminary assessment is subject to revisions to any additional guidance issued by the U.S. Treasury Department, Internal Revenue Service, FASB, and other standard-setting and regulatory bodies. Adjustments may materially impact our provision for income taxes and the assessment of the accounting for the tax effects of The Act will not extend beyond one year from the enactment date. 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 decreased $14.3 million during the year ended December 31, 2017 and increased $10.9 million and $11.7 million during the years ended December 31, 2016 and 2015 , respectively. 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, 2017 , the Company had net operating loss carryforwards of approximately $196.1 million and $91.8 million available to reduce future taxable income, if any, for federal and 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, 2017 , the Company had net research and development credit carryforwards of approximately $3.8 million and $3.2 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, 2017 , the Company had unrecognized tax benefits of $2.5 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, 2017 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, 2017 2016 2015 Unrecognized tax benefits, beginning of period $ 2,222 $ 1,871 $ 1,571 Gross increases—tax position in prior period — — — Gross decreases—tax position in prior period — — — Gross increases—current period tax position 301 351 300 Lapse of statute of limitations — — — Unrecognized tax benefits, end of period $ 2,523 $ 2,222 $ 1,871 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, 2017 . 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

401(k) Plan	12 Months Ended
	Dec. 31, 2017
Compensation and Retirement Disclosure [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 $324,000 , $262,000 and $103,000 for the years ended December 31, 2017 , 2016 , and 2015 , respectively.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	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, 2017 . 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 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 34,055,524 2016: Revenue $ 13,550 $ 14,675 $ 18,603 $ 18,257 Net loss (10,075 ) (11,243 ) (5,637 ) (4,403 ) Net loss per common share, basic and diluted (0.36 ) (0.40 ) (0.20 ) (0.14 ) Shares used to compute net loss per common share, basic and diluted 27,817,993 27,859,918 27,916,819 31,705,603

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
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"). The financial statements include the accounts of the Company and its former wholly-owned subsidiary, which was dissolved in June 2015. For periods prior to the subsidiary dissolution, all intercompany accounts and transactions were eliminated in consolidation.
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 $120,000 included in current assets as of December 31, 2016 , pledged for corporate cards. There was no such restricted amount as of December 31, 2017 . The Company also had deposits of $603,000 included in long-term assets as of December 31, 2017 and December 31, 2016 , 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.
Supplies Inventory	Supplies Inventory Supplies inventory consists of test reagents and other consumables primarily used in the sample collection kits and in cytopathology and genomic classifier test processing, and are valued at the lower of cost or market value. Cost is determined using actual costs on a first-in, first-out basis.
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 consists 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.
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.
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	Revenue Recognition The Company recognizes revenue in accordance with the provision of ASC 954-605, Health Care Entities—Revenue Recognition ("ASC 954") . The Company's revenue is generated from the provision of diagnostic services. The service is completed upon the delivery of test results to the prescribing physician, at which time the Company bills for the service. The Company recognizes revenue related to billings for tests delivered on an accrual basis when amounts that will ultimately be realized can be reasonably estimated. The estimates of amounts that will ultimately be realized requires significant judgment by management. Until a contract has been negotiated with a commercial payer or governmental program, the Company's tests may or may not be covered by these entities' existing reimbursement policies. In addition, patients do not enter into direct agreements with the Company that commit them to pay any portion of the cost of the tests in the event that their insurance declines to reimburse the Company. The Company may bill the patient directly for these amounts in the form of co-payments and co-insurance in accordance with their insurance carrier and health plans. In the absence of contracted reimbursement or the ability to estimate the amount that will ultimately be realized for the Company's services, revenue is recognized on the cash basis.
Cost of Revenue	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 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. Equity awards issued to non-employees are valued using the Black-Scholes option-pricing model and are 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 May 2014, the Financial Accounting Standards Board, or FASB, issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), to supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than are required under existing U.S. GAAP. The Company will adopt the new revenue standard as of January 1, 2018 using the modified retrospective method. The Company has completed its assessment of the five steps of this ASU and believes that the adoption of this ASU will not result in a material cumulative catch-up adjustment under the modified retrospective method, or have a material impact on the Company's financial position or results of operations. In February 2016, the FASB issued ASU No. 2016-2, Leases . 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. Entities are required to use a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited and early adoption is permitted. The Company is currently evaluating the potential effect of this standard on its financial statements. In March 2016, the FASB issued ASU 2016-9, Compensation - Stock Compensation , related to the tax effects of share-based awards. The ASU requires that all the tax effects of share-based awards be recorded through the income statement, thereby simplifying the current guidance that requires excess tax benefits and certain excess tax deficiencies to be recorded in equity. This ASU also permits an election for the impact of forfeitures on the recognition of expense for share-based payment awards where forfeitures can be estimated or recognized when they occur. This ASU was effective for interim and annual periods beginning after December 15, 2016. The Company adopted this ASU as of January 1, 2017 and elected to continue using its forfeiture estimation method for share-based payment awards. This ASU was adopted prospectively and the impact of adoption on the Company's financial statements was not material. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , provides specific guidance on cash flow classification issues, including classifying debt prepayment or debt extinguishment costs under financing activities in the statements of cash flows. The amendments in ASU 2016-15 are effective for interim and annual periods beginning after December 15, 2017. The ASU should be applied using a retrospective transition method, unless it is impracticable to do so for some of the issues. In such case, the amendments for those issues would be applied prospectively as of the earliest date practicable. Early adoption is permitted. This ASU was adopted retrospectively and the impact of adoption on the Company's financial statements was not material because prior period debt prepayment costs were immaterial and already included under financing activities in the statements of cash flows. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash. This ASU requires that restricted cash and restricted cash equivalents be 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 ASU will be effective for interim and annual periods beginning after December 15, 2017. The Company does not anticipate that the adoption of this ASU will have a significant impact on its financial statements.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Revenue Recognition
Schedule of Revenue recognized when cash is received and on an accrual basis	Revenue recognized for the years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands of dollars): Year Ended December 31, 2017 2016 2015 Revenue recognized on the accrual basis $ 69,274 96 % $ 47,099 72 % $ 27,043 55 % Revenue recognized on the cash basis 2,679 4 % 17,986 28 % 22,460 45 % Total $ 71,953 100 % $ 65,085 100 % $ 49,503 100 %
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, 2017 2016 2015 Medicare 26 % 27 % 26 % UnitedHealthcare 14 % 12 % 14 % 40 % 39 % 40 %
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: December 31, 2017 2016 Medicare 22 % 18 %

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share	The following outstanding common stock equivalents have been excluded from diluted net loss per common share for the years ended December 31, 2017 , 2016 and 2015 because their inclusion would be anti-dilutive: Year Ended December 31, 2017 2016 2015 Shares of common stock subject to outstanding options 6,163,734 5,093,454 4,086,640 Employee stock purchase plan 34,559 36,651 15,561 Restricted stock units 63,425 25,000 — Total common stock equivalents 6,261,718 5,155,105 4,102,201

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Schedule of property and equipment	Property and equipment consisted of the following (in thousands of dollars): Year Ended December 31, 2017 2016 Leasehold improvements $ 5,790 $ 5,861 Laboratory equipment 8,026 6,441 Computer equipment 1,293 1,177 Software, including software developed for internal use 2,308 1,937 Furniture and fixtures 1,435 1,131 Construction-in-process 141 1,769 Total property and equipment, at cost 18,993 18,316 Accumulated depreciation and amortization (9,305 ) (6,836 ) Total property and equipment, net $ 9,688 $ 11,480
Schedule of accrued liabilities	Accrued liabilities consisted of the following (in thousands of dollars): Year Ended December 31, 2017 2016 Accrued compensation expense $ 5,293 $ 6,120 Accrued other 2,882 2,990 Total accrued liabilities $ 8,175 $ 9,110

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2017 are as follows (in thousands of dollars): Year Ending December 31, Amounts 2018 $ 2,121 2019 2,227 2020 2,332 2021 2,401 2022 2,472 Thereafter 9,384 Total minimum lease payments $ 20,937

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
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 net debt obligation	As of December 31, 2017 , the net debt obligation for borrowings made under the Loan and Security Agreement was as follows (in thousands of dollars): December 31, 2017 Debt principal $ 25,000 End-of-term debt obligation 53 Unamortized debt issuance costs (115 ) Net debt obligation $ 24,938 As of December 31, 2016 , the net debt obligation for borrowings made under the Loan and Security Agreement was as follows (in thousands of dollars): December 31, 2016 Debt principal $ 25,385 Unamortized debt issuance costs (467 ) Net debt obligation $ 24,918
Schedule of interest expense on debt	Interest expense was recognized as follows (in thousands of dollars): Year Ended December 31, 2017 2016 2015 Nominal debt interest $ 2,838 $ 2,378 $ 253 Amortization and write-off of debt discount and issuance costs 472 173 46 End-of-term debt obligation interest 53 156 79 Debt prepayment penalty 1,536 50 — Interest on capital lease 42 — — Total $ 4,941 $ 2,757 $ 378

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of reserved shares of common stock for issuance	As of December 31, 2017 and 2016 , the Company had reserved shares of common stock for issuance as follows: December 31, 2017 2016 Stock options and restricted stock units issued and outstanding 6,061,081 5,251,832 Stock options and restricted stock units available for grant under stock option plans 1,133,907 887,724 Common stock available for the Employee Stock Purchase Plan 456,002 609,053 Total 7,650,990 6,748,609

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2017
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 Weighted Weighted Average Aggregate Balance—December 31, 2016 887,724 5,251,832 $ 7.56 7.24 $ 8,515 Additional shares authorized 1,350,491 — Granted - stock options (1,769,000 ) 1,769,000 8.80 Granted - restricted stock units (60,000 ) 60,000 Canceled 715,297 (715,297 ) 9.94 Exercised — (279,454 ) 5.13 Restricted stock units vested — (25,000 ) Tax portion of restricted stock units vested 9,395 — Balance—December 31, 2017 1,133,907 6,061,081 $ 7.76 6.71 $ 4,531 Options vested and exercisable—December 31, 2017 3,174,848 $ 7.43 5.58 $ 4,257 Options vested and expected to vest—December 31, 2017 5,749,963 $ 7.74 6.64 $ 4,509
Stock-based Compensation
Stock incentive plans
Summary of share-based compensation expense	The following table summarizes stock-based compensation expense related to stock options, restricted stock units and the ESPP for the years ended December 31, 2017, 2016 and 2015, and are included in the statements of operations and comprehensive loss as follows (in thousands of dollars): Year Ended December 31, 2017 2016 2015 Cost of revenue $ 133 $ 126 $ 100 Research and development 1,495 1,322 1,178 Selling and marketing 1,899 1,594 1,326 General and administrative 3,090 3,336 2,998 Total stock-based compensation expense $ 6,617 $ 6,378 $ 5,602
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, 2017 2016 2015 Weighted-average volatility 50.40 - 52.40% 52.49 - 56.36% 52.56 - 68.82% Weighted-average expected term (years) 5.50 - 6.08 5.50 - 6.27 5.50 - 6.08 Risk-free interest rate 1.80 - 2.33% 1.16 - 2.09% 1.55 - 2.03% 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, 2017 2016 2015 Weighted-average volatility 50.40 - 51.10% 52.77 - 65.85% 64.72 - 74.48% Weighted-average expected term (years) 6.80 - 7.75 7.80 - 8.56 7.92 - 10.00 Risk-free interest rate 2.16 - 2.37% 1.39 - 2.30% 1.78 - 2.29% Expected dividend yield — — —
ESPP
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, 2017 2016 2015 Weighted-average volatility 37.00 - 43.86% 46.38 - 75.72% 53.57 - 58.10% Weighted-average expected term (years) 0.50 - 1.00 0.50 - 1.00 0.49 - 0.99 Risk-free interest rate 0.65 - 1.22% 0.40 - 0.50% 0.17 - 0.33% Expected dividend yield — — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2017 2016 2015 U.S. federal taxes at statutory rate $ (10,541 ) $ (10,662 ) $ (11,459 ) State tax (net of federal benefit) 15 20 (30 ) Permanent differences 198 153 96 Incentive stock options 994 1,095 789 Tax credits (588 ) (677 ) (581 ) Change in valuation allowance (14,552 ) 10,071 11,185 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, 2017 2016 2015 Deferred tax assets: Net operating loss carryforwards $ 47,177 $ 61,674 $ 52,262 Research and development credits 4,034 3,174 2,497 Stock-based compensation 2,068 2,847 1,825 Genzyme co-promotion agreement — — 330 Accruals, deferred rent and other 2,375 4,511 4,698 Gross deferred tax assets 55,654 72,206 61,612 Valuation allowance (51,657 ) (65,975 ) (55,101 ) Net deferred tax assets 3,997 6,231 6,511 Deferred tax liabilities: Property and equipment (983 ) (1,180 ) (1,215 ) In-process research and development (3,014 ) (5,051 ) (5,296 ) Gross deferred tax liabilities (3,997 ) (6,231 ) (6,511 ) Net deferred tax liabilities (3,997 ) (6,231 ) (6,511 ) 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, 2017 2016 2015 Unrecognized tax benefits, beginning of period $ 2,222 $ 1,871 $ 1,571 Gross increases—tax position in prior period — — — Gross decreases—tax position in prior period — — — Gross increases—current period tax position 301 351 300 Lapse of statute of limitations — — — Unrecognized tax benefits, end of period $ 2,523 $ 2,222 $ 1,871

Selected Quarterly Financial 30

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
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 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 34,055,524 2016: Revenue $ 13,550 $ 14,675 $ 18,603 $ 18,257 Net loss (10,075 ) (11,243 ) (5,637 ) (4,403 ) Net loss per common share, basic and diluted (0.36 ) (0.40 ) (0.20 ) (0.14 ) Shares used to compute net loss per common share, basic and diluted 27,817,993 27,859,918 27,916,819 31,705,603

Organization and Description 31

Organization and Description of Business (Details)	12 Months Ended
	Dec. 31, 2017segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Operating Segments	1

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Liquidity (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2017USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Liquidity
Number of Operating Segments | segment		1
Liquidity
Accumulated deficit		$ 211,087	$ 180,084
Cash and cash equivalents		$ 33,891	$ 59,219	$ 39,084	$ 35,014
Revolving Credit Facility | Line of Credit | Silicon Valley Bank
Liquidity
Proceeds from long-term lines of credit	$ 25,000

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Credit Risk, Restricted Cash, and Allowance for Doubtful Accounts (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Institution	Dec. 31, 2016USD ($)	Dec. 31, 2015
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 | Institution	1
Restricted Cash
Long term deposit consisting of letter of credit serving as security for lease	$ 603	$ 603
Headquarters and laboratory facilities, South San Francisco, Lease expiring 2016
Restricted Cash
Amount held as security for lease		120
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
Amount held as security for lease	603	$ 603
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)	40.00%	39.00%	40.00%
Revenue | Revenue concentration risk | Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	26.00%	27.00%	26.00%
Revenue | Revenue concentration risk | United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	14.00%	12.00%	14.00%
Accounts receivable | Gross receivables concentration risk | Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	22.00%	18.00%

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Intangible Assets, Bonus Accruals, and Revenue Recongition (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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									$ 69,274,000	$ 47,099,000	$ 27,043,000
Revenue recognized on accrual basis, percentage									96.00%	72.00%	55.00%
Revenue recognized on a cash basis									$ 2,679,000	$ 17,986,000	$ 22,460,000
Revenue recognized on a cash basis, percentage									4.00%	28.00%	45.00%
Total	$ 19,596,000	$ 17,519,000	$ 18,406,000	$ 16,432,000	$ 18,257,000	$ 18,603,000	$ 14,675,000	$ 13,550,000	$ 71,953,000	$ 65,085,000	$ 49,503,000
Total, Percent									100.00%	100.00%	100.00%
Net loss per common share, basic and diluted (in dollars per share)	$ (0.24)	$ (0.21)	$ (0.22)	$ (0.24)	$ (0.14)	$ (0.20)	$ (0.40)	$ (0.36)	$ (0.91)	$ (1.09)	$ (1.30)
Accrued Income Receivable
Revenue Recognition
Total						$ 3,500,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Property, plant and equipment, useful life (in years)									3 years
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Property, plant and equipment, useful life (in years)									5 years

Net Loss Per Share (Details)

Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	6,261,718	5,155,105	4,102,201
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	6,163,734	5,093,454	4,086,640
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	34,559	36,651	15,561
Restricted stock units (RSUs)
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	63,425	25,000	0

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property and Equipment, Net
Total property and equipment, at cost	$ 18,993,000	$ 18,316,000
Accumulated depreciation and amortization	(9,305,000)	(6,836,000)
Total property and equipment, net	9,688,000	11,480,000
Depreciation and amortization expense	2,800,000	2,400,000	$ 1,500,000
Capital leases, accumulated depreciation	135,000
Capital leases, depreciation expense	135,000
Leasehold improvements
Property and Equipment, Net
Total property and equipment, at cost	5,790,000	5,861,000
Laboratory equipment
Property and Equipment, Net
Total property and equipment, at cost	8,026,000	6,441,000
Capital leased assets	1,200,000	1,200,000
Computer equipment
Property and Equipment, Net
Total property and equipment, at cost	1,293,000	1,177,000
Software, including software developed for internal use
Property and Equipment, Net
Total property and equipment, at cost	2,308,000	1,937,000
Furniture and fixtures
Property and Equipment, Net
Total property and equipment, at cost	1,435,000	1,131,000
Construction-in-process
Property and Equipment, Net
Total property and equipment, at cost	$ 141,000	$ 1,769,000

Balance Sheet Components- Finit

Balance Sheet Components- Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance Sheet Related Disclosures [Abstract]
Useful life	15 years
Annual amortization expense expected to be recognized	$ 1.1	$ 1.1	$ 0.8
Intangible asset amortization	$ 3	$ 1.9	$ 0.8

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities
Accrued compensation expenses	$ 5,293	$ 6,120
Accrued other	2,882	2,990
Total accrued liabilities	$ 8,175	$ 9,110

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Money Market Funds | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 33,100	$ 58,700
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

Commitments and Contingencies40

Commitments and Contingencies (Details) ft² in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 30, 2015ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Future minimum lease payments under non-cancelable operating leases
2,018		$ 2,121
2,019		2,227
2,020		2,332
2,021		2,401
2,022		2,472
Thereafter		9,384
Total minimum lease payments		20,937
Facilities rent expense		1,900	$ 2,000	$ 1,900
Supplies Purchase Commitments
Non-cancelable purchase commitment		7,100
Headquarters and laboratory facilities, South San Francisco, Lease signed in April 2015
Operating Leases
Amount of space leased | ft²	59
Security deposit		603	603
Laboratory facilities, Austin, Texas
Operating Leases
Security deposit		$ 139	$ 75

Commitments and Contingencies C

Commitments and Contingencies Capital Lease (Details) - Equipment - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
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
Future minimum payments due, 2018	317
Future minimum payments due, 2019	$ 317

Debt Loan and Security Agreemen

Debt Loan and Security Agreement (Details) - Line of Credit - Silicon Valley Bank - USD ($)	Nov. 03, 2017	Dec. 31, 2017
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 35,000,000
Liquidity Requirement, Minimum		$ 40,000,000
Secured Debt
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	25,000,000
Periodic payment terms, balloon payment to be paid	1,200,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 10,000,000
London Interbank Offered Rate (LIBOR) | Secured Debt
Line of Credit Facility [Line Items]
Basis spread on variable rate	4.20%
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.50%
Minimum | London Interbank Offered Rate (LIBOR) | Secured Debt
Line of Credit Facility [Line Items]
Interest rate, stated percentage	5.43%
Minimum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Interest rate, stated percentage	4.70%
Debt Prepayment Tranche One | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Prepayment premium		750,000
Debt Prepayment Tranche Two | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Prepayment premium		500,000
Debt Prepayment Tranche Three | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Line of Credit Facility [Line Items]
Prepayment premium		$ 250,000

Debt Loan and Security Agreem43

Debt Loan and Security Agreement- Tabular (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Interest on end-of-term debt obligation and prepayment penalty	$ 53	$ 156	$ 79
Line of Credit
Debt Instrument [Line Items]
Debt principal	26,187
Interest on end-of-term debt obligation and prepayment penalty	53
Debt instrument, unamortized discount	(115)	(467)
Long-term debt	24,938	$ 24,918
2,019	1,389
2,020	8,333
2,021	8,333
2,022	$ 8,132

Debt Credit Agreement (Details)

Debt Credit Agreement (Details)	Nov. 03, 2017USD ($)	Mar. 30, 2016USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2017USD ($)installmentloan	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
Repayments of long-term debt				$ 25,385,000	$ 5,000,000	$ 0
Conversion of accrued interest to long-term debt				0	385,000	0
Payment of End of Term Obligation				$ 1,536,000	$ 288,000	$ 0
Visium | Line of Credit
Debt Instrument [Line Items]
Number of term loans | loan				2
Line of credit facility, maximum borrowing capacity				$ 40,000,000
Repayments of long-term debt	$ 27,300,000
Interest rate, stated percentage				12.00%
Number of installments | installment				8
Term of debt with equal quarterly installments				2 years
Debt Instrument Penalty Percentage On Prepayment Period One				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
Payment of End of Term Obligation	$ 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 Credit Agreement- Tabular

Debt Credit Agreement- Tabular (Details) - Line of Credit - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Debt instrument, face amount	$ 25,000,000	$ 25,385,000
Debt instrument, unamortized discount	(115,000)	(467,000)
Long-term debt	$ 24,938,000	$ 24,918,000

Interest Expense (Details)

Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Nominal interest	$ 2,838	$ 2,378	$ 253
Amortization and write-off of debt discount and issuance costs	472	173	46
End-of-term debt obligation interest	53	156	79
Debt prepayment penalty	1,536	50	0
Interest on capital lease	42	0	0
Total	$ 4,941	$ 2,757	$ 378

Stockholders' Equity (Details)

Stockholders' Equity (Details)	1 Months Ended			12 Months Ended
	Nov. 30, 2016USD ($)$ / sharesshares	May 31, 2015USD ($)	Apr. 30, 2015USD ($)$ / sharesshares	Dec. 31, 2017USD ($)vote$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)shares
Common Stock
Authorized shares of common stock				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 | vote				1
Dividends declared | $				$ 0
Options issued and outstanding (in shares)				6,061,081	5,251,832
Shares available for issuance				1,133,907	887,724
Total number of shares reserved for issuance				7,650,990	6,748,609
Common stock, shares issued				34,210,388	33,762,278
Net proceeds from sale of common stock in private placement | $				$ 0	$ 0	$ 37,258,000
Options
Common Stock
Options issued and outstanding (in shares)				6,061,081	5,251,832
Shares available for issuance				1,133,907	887,724
ESPP
Employee Stock Purchase Plan
Maximum offering period		12 months
Purchase period		6 months
Maximum fair market value of shares an employee can purchase per calendar year | $		$ 25,000
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)				37.00%	46.38%	53.57%
Weighted-average volatility, high end of range (as a percent)				43.86%	75.72%	58.10%
Risk-free interest rate, low end of range (as a percent)				0.65%	0.40%	0.17%
Risk-free interest rate, high end of range (as a percent)				1.22%	0.50%	0.33%
ESPP | Minimum
Employee Stock Purchase Plan
Minimum purchase price as a percentage of fair market value		85.00%
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term				6 months	6 months	5 months 27 days
ESPP | Maximum
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term				1 year	1 year	11 months 27 days
Common Stock
Common Stock
Common stock, shares issued	5,723,300
Shares issued, price per share (in usd per share) | $ / shares	$ 6
Proceeds from issuance of common stock | $	$ 32,100,000
Payments of stock issuance costs | $	$ 2,200,000
Number of common stock issued and sold in private placement					5,723,300	4,907,975
Share Price (in usd per share) | $ / shares				$ 6.53	$ 7.74
Common Stock | Private placement
Common Stock
Number of common stock issued and sold in private placement			4,907,975
Share Price (in usd per share) | $ / shares			$ 8.15
Net proceeds from sale of common stock in private placement | $			$ 37,300,000
Agent fees and other expenses | $			$ 2,700,000
Common Stock | ESPP
Common Stock
Shares available for issuance				456,002	609,053
Prepaid Expenses and Other Current Assets
Common Stock
Accounts receivable | $					$ 200,000

Stock Incentive Plans - Stock O

Stock Incentive Plans - Stock Option Plans (Details) - shares	1 Months Ended	12 Months Ended
	Feb. 29, 2008	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2013
Stock incentive plans
Number of shares available for issuance		1,133,907	887,724
Options
Stock incentive plans
Number of shares available for issuance		1,133,907	887,724
2008 Plan | Options | Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value	100.00%
2008 Plan | Options | Maximum
Stock incentive plans
Term of options granted	10 years
2008 Plan | ISO | Minimum
Stock incentive plans
Voting power of person owning stock (as a percent)	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
Stock Incentive Plan 2013
Stock incentive plans
Number of additional shares reserved for issuance				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		1,133,907
Stock Incentive Plan 2013 | Options | Outside director serving as a member of Board of Directors for at least six months
Stock incentive plans
Shares granted as annual grant		10,000
Stock Incentive Plan 2013 | 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 | Options | Outside director
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
Stock Incentive Plan 2013 | Options | Outside director | Maximum
Stock incentive plans
Expiration period after termination of service		12 months
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		35,000
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 - Activit

Stock Incentive Plans - Activity Under Stock Option Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares Available for Grant
Balance at the beginning of the period (in shares)	887,724
Additional options authorized (in shares)	1,350,491
Canceled (in shares)	715,297
Balance at the end of the period (in shares)	1,133,907	887,724
Stock Options Outstanding
Balance at beginning of the period (in shares)	5,251,832
Canceled (in shares)	(715,297)
Exercised (in shares)	(279,454)
Balance at the end of the period (in shares)	6,061,081	5,251,832
Options vested and exercisable at the end of the period (in shares)	3,174,848
Options vested and expected to vest at the end of the period (in shares)	5,749,963
Weighted Average Exercise Price
Balance at beginning of the period (in dollars per share)	$ 7.56
Canceled (in dollars per share)	9.94
Exercised (in dollars per share)	5.13
Balance at the end of the period (in dollars per share)	7.76	$ 7.56
Options vested and exercisable at the end of the period (in dollars per share)	7.43
Options vested and expected to vest at the end of the period (in dollars per share)	$ 7.74
Weighted Average Remaining Contractual Life
Balance	6 years 8 months 16 days	7 years 2 months 26 days
Options vested and exercisable at the end of the period	5 years 6 months 29 days
Options vested and expected to vest at the end of the period	6 years 7 months 21 days
Aggregate Intrinsic Value
Balance at the beginning of the period (in dollars)	$ 8,515,000
Balance at the end of the period (in dollars)	4,531,000	$ 8,515,000
Options vested and exercisable at the end of the period (in dollars)	4,257,000
Options vested and expected to vest at the end of the period (in dollars)	$ 4,509,000
Employee stock options
Shares Available for Grant
Granted (in shares)	(1,769,000)
Stock Options Outstanding
Granted (in shares)	1,769,000
Weighted Average Exercise Price
Granted (in dollars per share)	$ 8.80
Restricted stock units (RSUs)
Shares Available for Grant
Granted (in shares)	(60,000)
Tax portion of restricted stock units vested (in shares)	9,395
Stock Options Outstanding
Granted (in shares)	60,000
Vested (in shares)	(25,000)
Aggregate Intrinsic Value
Options vested and expected to vest at the end of the period (in dollars)	$ 157,000

Stock Incentive Plans - Additio

Stock Incentive Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock incentive plans
Weighted average fair value of options to purchase common stock granted (in dollars per share)	$ 4.49	$ 3.35	$ 5.12
Intrinsic value of stock options exercised (in dollars)	$ 700,000	$ 900,000	$ 1,800,000
Weighted average grant date fair value (in usd per share)	$ 8.93	$ 7.47
Intrinsic value of stock options outstanding	$ 4,509,000
Common Stock
Stock incentive plans
Share Price (in usd per share)	$ 6.53	$ 7.74
Employee stock options
Stock incentive plans
Total estimated grant date fair value of options to purchase common stock vested (in dollars)	$ 3,100,000	$ 5,800,000	$ 5,300,000
Restricted stock units (RSUs)
Stock incentive plans
Intrinsic value of stock options outstanding	$ 157,000

Stock Incentive Plans Stock Inc

Stock Incentive Plans Stock Incentive Plans- ESPP (Details) - ESPP	1 Months Ended
	May 31, 2015USD ($)
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-b

Stock Incentive Plans - Stock-based Compensation (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 29, 2008	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based Compensation
Stock-based compensation
Share-based compensation expense (in dollars)		$ 6,617	$ 6,378	$ 5,602
Unrecognized compensation expense (in dollars)		$ 9,200
Period over which unrecognized compensation expense expected to be recognized		2 years 6 months
Stock-based Compensation | Cost of revenue
Stock-based compensation
Share-based compensation expense (in dollars)		$ 133	126	100
Stock-based Compensation | Research and development
Stock-based compensation
Share-based compensation expense (in dollars)		1,495	1,322	1,178
Stock-based Compensation | Selling and marketing
Stock-based compensation
Share-based compensation expense (in dollars)		1,899	1,594	1,326
Stock-based Compensation | General and administrative
Stock-based compensation
Share-based compensation expense (in dollars)		$ 3,090	$ 3,336	$ 2,998
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)		50.40%	52.49%	52.56%
Weighted-average volatility, high end of range (as a percent)		52.40%	56.36%	68.82%
Risk-free interest rate, low end of range (as a percent)		1.80%	1.16%	1.55%
Risk-free interest rate, high end of range (as a percent)		2.33%	2.09%	2.03%
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)		50.40%	52.77%	64.72%
Weighted-average volatility, high end of range (as a percent)		51.10%	65.85%	74.48%
Risk-free interest rate, low end of range (as a percent)		2.16%	1.39%	1.78%
Risk-free interest rate, high end of range (as a percent)		2.37%	2.30%	2.29%
ESPP
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)		37.00%	46.38%	53.57%
Weighted-average volatility, high end of range (as a percent)		43.86%	75.72%	58.10%
Risk-free interest rate, low end of range (as a percent)		0.65%	0.40%	0.17%
Risk-free interest rate, high end of range (as a percent)		1.22%	0.50%	0.33%
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		5 years 6 months	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		6 years 9 months 18 days	7 years 9 months 18 days	7 years 11 months 1 day
Minimum | ESPP
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term		6 months	6 months	5 months 27 days
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		6 years 29 days	6 years 3 months 7 days	6 years 29 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		7 years 9 months	8 years 6 months 22 days	10 years
Maximum | ESPP
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term		1 year	1 year	11 months 27 days
2008 Plan | Maximum | Options
Stock-based compensation
Term of options granted	10 years
2008 Plan | Maximum | ISO
Stock-based compensation
Term of options granted to a person owning stock representing more than 10% of voting power of all classes of stock	5 years

Genzyme Co-promotion Agreement

Genzyme Co-promotion Agreement (Details)	Jan. 01, 2015	Feb. 29, 2012USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Feb. 28, 2015country	Jan. 31, 2012country
Genzyme Co-promotion Agreement
Amortization of up-front co-promotion fee			$ 0	$ 948,000	$ 1,897,000
Co-promotion agreement | Genzyme
Genzyme Co-promotion Agreement
Co-promotion expenses				6,100,000	7,300,000
Outstanding obligation to Genzyme			$ 0	0
Amortization of up-front co-promotion fee				$ 900,000	$ 1,900,000
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
Co-promotion fee received from Genzyme		$ 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
Co-promotion fee paid as a percentage of net revenue	25.00%
Period of agreement	5 years

Thyroid Cytopathology Partners

Thyroid Cytopathology Partners (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Oct. 16, 2017USD ($)installment
Thyroid Cytopathology Partners
Outstanding obligations	$ 3,853,000	$ 2,424,000
Prepaid expenses and other current assets	1,997,000	2,057,000
Other assets	$ 326,000	134,000
Thyroid Cytopathology Partners
Thyroid Cytopathology Partners
Contract termination fee				$ 1,800,000
Payment Installments for Contract Termination Fee | installment				8
Notice of intent not to renew period	12 months
Expenses for cytopathology testing and evaluation services	$ 4,600,000	5,100,000	$ 4,700,000
Outstanding obligations	308,000	426,000
Reduction to rent expense for TCP's portion of costs for shared space	$ (114,000)	$ (103,000)	$ (90,000)

Income Taxes - Tax Effects (Det

Income Taxes - Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Pretax loss	$ 31,000	$ 31,400	$ 33,700
Reconciliation of tax expense computed at the statutory federal rate and the Company's tax expense
U.S. federal taxes at statutory rate	(10,541)	(10,662)	(11,459)
State tax (net of federal benefit)	15	20	(30)
Permanent differences	198	153	96
Incentive stock options	994	1,095	789
Tax credits	(588)	(677)	(581)
Change in valuation allowance	(14,552)	10,071	11,185
Rate differential impact - Tax Cuts and Jobs Act	24,474	0	0
Total provision for income taxes	0	0	0
Non-current deferred tax assets:
Net operating loss carryforwards	47,177	61,674	52,262
Research and development credits	4,034	3,174	2,497
Stock-based compensation	2,068	2,847	1,825
Genzyme co-promotion agreement	0	0	330
Accruals, deferred rent and other	2,375	4,511	4,698
Gross deferred tax assets	55,654	72,206	61,612
Valuation allowance	(51,657)	(65,975)	(55,101)
Net deferred tax assets	3,997	6,231	6,511
Deferred tax liabilities:
Property and equipment	(983)	(1,180)	(1,215)
In-process research and development	(3,014)	(5,051)	(5,296)
Gross deferred tax liabilities	(3,997)	(6,231)	(6,511)
Net deferred tax liabilities	(3,997)	(6,231)	(6,511)
Net deferred taxes	0	0	0
Tax Cuts And Jobs Act Of 2017, deferred tax asset decrease	24,500
Increase in valuation allowance against deferred tax assets	14,300	$ (10,900)	$ (11,700)
Share-based compensation excess tax benefit amount	1,600
Federal
Operating loss carryforwards
Net operating loss carryforwards	196,100
State
Operating loss carryforwards
Net operating loss carryforwards	$ 91,800

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Unrecognized tax benefits, beginning of period	$ 2,222	$ 1,871	$ 1,571
Gross increases-tax position in prior period	0	0	0
Gross decreases—tax position in prior period	0	0	0
Gross increases-current period tax position	301	351	300
Lapse of statute of limitations	0	0	0
Unrecognized tax benefits, end of period	2,523	$ 2,222	$ 1,871
Interest expense or penalties related to unrecognized tax benefits	0
Federal
Credit carryforwards
Credit carryforwards available to reduce future taxable income	3,800
State
Credit carryforwards
Credit carryforwards available to reduce future taxable income	$ 3,200

Income Taxes - Income Tax Exami

Income Taxes - Income Tax Examination (Details)	12 Months Ended
	Dec. 31, 2017
Federal
Income tax examination
Income tax examination period	3 years
State
Income tax examination
Income tax examination period	4 years

401(k) Plan (Details)

401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employer contributions to the plan	$ 324	$ 262	$ 103

Selected Quarterly Financial 59

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Data (Unaudited)
Total revenues	$ 19,596	$ 17,519	$ 18,406	$ 16,432	$ 18,257	$ 18,603	$ 14,675	$ 13,550	$ 71,953	$ 65,085	$ 49,503
Net loss	$ (8,439)	$ (7,049)	$ (7,298)	$ (8,217)	$ (4,403)	$ (5,637)	$ (11,243)	$ (10,075)	$ (31,003)	$ (31,358)	$ (33,704)
Net loss per common share, basic and diluted	$ (0.24)	$ (0.21)	$ (0.22)	$ (0.24)	$ (0.14)	$ (0.20)	$ (0.40)	$ (0.36)	$ (0.91)	$ (1.09)	$ (1.30)
Shares use to compute net loss per common share, basic and diluted (in shares)	34,055,524	33,946,748	33,873,128	33,823,889	31,705,603	27,916,819	27,859,918	27,817,993	33,925,617	28,830,472	25,994,193