Histogen (HSTO) S-4/A 13 Mar 20 Registration of securities issued in business combination transactions (amended) Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2019
Cover [Abstract]
Document Type	S-4/A
Amendment Flag	false
Entity Registrant Name	CONATUS PHARMACEUTICALS INC.
Entity Central Index Key	0001383701
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	16745 West Bernardo Dr.
Entity Address, Address Line Two	Suite 250
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92127
City Area Code	(858)
Local Phone Number	376-2600

Balance Sheets

Balance Sheets - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 20,703,000	$ 11,565,000
Marketable securities	0	29,127,000
Collaboration receivables	122,000	3,677,000
Prepaid and other current assets	781,000	3,057,000
Total current assets	21,606,000	47,426,000
Property and equipment, net	0	154,000
Other assets	221,000	1,223,000
Total assets	21,827,000	48,803,000
Current liabilities:
Accounts payable and accrued expenses	1,064,000	6,216,000
Accrued compensation	238,000	2,230,000
Current portion of deferred revenue	0	10,075,000
Current portion of lease liabilities	338,000	0
Total current liabilities	1,640,000	18,521,000
Deferred revenue, less current portion	0	2,815,000
Deferred rent, less current portion	0	68,000
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.0001 par value; 200,000 shares authorized; 33,170 shares and 33,165 shares issued and outstanding at December 31, 2019 and 2018, respectively	3,000	3,000
Additional paid-in capital	218,198,000	214,042,000
Accumulated other comprehensive loss	0	(17,000)
Accumulated deficit	(198,014,000)	(186,629,000)
Total stockholders’ equity	20,187,000	27,399,000
Total liabilities and stockholders’ equity	$ 21,827,000	$ 48,803,000

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	33,170,000	33,165,000
Common stock, shares outstanding	33,170,000	33,165,000

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Collaboration revenue	$ 21,717	$ 33,586	$ 35,377
Total revenues	21,717	33,586	35,377
Operating expenses:
Research and development	23,527	41,368	43,220
General and administrative	10,196	10,495	9,707
Total operating expenses	33,723	51,863	52,927
Loss from operations	(12,006)	(18,277)	(17,550)
Other income (expense):
Interest income	568	962	892
Interest expense	0	(696)	(662)
Other income (expense)	53	1	(76)
Total other income	621	267	154
Net loss	(11,385)	(18,010)	(17,396)
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities	17	60	(71)
Comprehensive loss	$ (11,368)	$ (17,950)	$ (17,467)
Net loss per share, basic and diluted	$ (0.34)	$ (0.59)	$ (0.61)
Weighted average shares outstanding used in computing net loss per share, basic and diluted	33,169	30,370	28,587

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2016	$ 21,789	$ 3	$ 172,425	$ (6)	$ (150,633)
Beginning balance, shares at Dec. 31, 2016		26,119
Issuance of common stock upon exercise of stock options	$ 104	$ 0	104	0	0
Issuance of common stock upon exercise of stock options, shares	79	79
Issuance of common stock for employee stock purchase plan	$ 65	$ 0	65	0	0
Issuance of common stock for employee stock purchase plan, shares		24
Share-based compensation	4,098	$ 0	4,076	0	22
Issuance of common stock, net of offering costs	30,610	$ 0	30,610	0	0
Issuance of common stock, net of offering costs, shares		5,980
Repurchase of common stock	(11,203)	$ 0	(11,203)	0	0
Repurchase of common stock, shares		(2,167)
Net loss	(17,396)	$ 0	0	0	(17,396)
Unrealized gain (loss) on marketable securities	(71)	0	0	(71)	0
Ending balance at Dec. 31, 2017	27,996	$ 3	196,077	(77)	(168,007)
Ending balance, shares at Dec. 31, 2017		30,035
Issuance of common stock upon exercise of stock options	$ 362	$ 0	362	0	0
Issuance of common stock upon exercise of stock options, shares	211	211
Issuance of common stock for employee stock purchase plan	$ 117	$ 0	117	0	0
Issuance of common stock for employee stock purchase plan, shares		36
Share-based compensation	3,757	$ 0	3,757	0	0
Conversion of convertible note payable to common stock	13,729	$ 0	13,729	0	0
Conversion of convertible note payable to common stock, shares		2,883
Cumulative effect of adoption of accounting standard	(612)	$ 0	0	0	(612)
Net loss	(18,010)	0	0	0	(18,010)
Unrealized gain (loss) on marketable securities	60	0	0	60	0
Ending balance at Dec. 31, 2018	$ 27,399	$ 3	214,042	(17)	(186,629)
Ending balance, shares at Dec. 31, 2018		33,165
Issuance of common stock upon exercise of stock options, shares	0
Issuance of common stock for employee stock purchase plan	$ 3	$ 0	3	0	0
Issuance of common stock for employee stock purchase plan, shares		5
Share-based compensation	4,153	$ 0	4,153	0	0
Net loss	(11,385)	0	0	0	(11,385)
Unrealized gain (loss) on marketable securities	17	0	0	17	0
Ending balance at Dec. 31, 2019	$ 20,187	$ 3	$ 218,198	$ 0	$ (198,014)
Ending balance, shares at Dec. 31, 2019		33,170

Statements of Cash Flows

Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (11,385,000)	$ (18,010,000)	$ (17,396,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	73,000	91,000	108,000
Stock-based compensation expense	4,153,000	3,757,000	4,098,000
Amortization of premiums and discounts on marketable securities, net	(204,000)	(341,000)	(68,000)
Write off of property and equipment and other assets	210,000	0	0
Impairment of right-of-use asset	50,000	0	0
Accrued interest included in convertible note payable	0	696,000	658,000
Changes in operating assets and liabilities:
Collaboration receivables	3,555,000	(310,000)	(867,000)
Prepaid and other current assets	642,000	480,000	(123,000)
Other assets	0	(537,000)	(872,000)
Accounts payable and accrued expenses	(2,355,000)	(5,760,000)	6,638,000
Accrued compensation	(1,992,000)	222,000	(343,000)
Deferred revenue	(12,890,000)	(15,099,000)	(25,010,000)
Lease liabilities, net	(59,000)	0	0
Deferred rent	0	(46,000)	(32,000)
Net cash used in operating activities	(20,202,000)	(34,857,000)	(33,209,000)
Investing activities
Maturities of marketable securities	44,842,000	69,685,000	81,877,000
Purchase of marketable securities	(15,494,000)	(39,637,000)	(121,723,000)
Capital expenditures	(11,000)	(66,000)	(25,000)
Net cash provided by (used in) investing activities	29,337,000	29,982,000	(39,871,000)
Financing activities
Proceeds from issuance of convertible note payable, net	0	0	12,500,000
Principal payment on promissory note	0	0	(1,000,000)
Proceeds from issuance of common stock, net	0	0	30,610,000
Repurchase of common stock	0	0	(11,203,000)
Deferred financing costs	0	(118,000)	0
Proceeds from stock issuances related to exercise of stock options and employee stock purchase plan	3,000	479,000	169,000
Net cash provided by financing activities	3,000	361,000	31,076,000
Net (decrease) increase in cash and cash equivalents	9,138,000	(4,514,000)	(42,004,000)
Cash and cash equivalents at beginning of period	11,565,000	16,079,000	58,083,000
Cash and cash equivalents at end of period	20,703,000	11,565,000	16,079,000
Supplemental disclosure of cash flow information:
Cash paid for interest	0	0	5,000
Supplemental schedule of noncash financing activities:
Conversion of convertible note payable to common stock	0	13,729,000	0
Right-of-use asset	$ 590,000	$ 0	$ 0

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Conatus Pharmaceuticals Inc. (the Company) was incorporated in the state of Delaware on July 13, 2005. The Company is a biotechnology company that has been focused on the development and commercialization of novel medicines to treat chronic diseases with significant unmet need. In December 2016, the Company entered into an Option, Collaboration and License Agreement (the Collaboration Agreement) with Novartis Pharma AG (Novartis) for the development and commercialization of emricasan, an orally active pan-caspase inhibitor, for the treatment of patients with chronic liver disease. In March 2019, the Company announced that top-line results from the ENCORE-NF clinical trial of emricasan did not meet the primary endpoint. In June 2019, the Company announced that top-line results from its ENCORE-LF clinical trial of emricasan also did not meet the primary endpoint. In addition, results from the 24-week extension in the Company’s ENCORE-PH clinical trial of emricasan were consistent with results from the initial 24-week treatment period and did not meet predefined objectives. Consequently, the Company and Novartis have no further development plans for emricasan, and the Company and Novartis entered into an amendment to the Collaboration Agreement, pursuant to which the Company and Novartis mutually agreed to terminate the Collaboration Agreement, effective September 30, 2019. In order to extend the Company’s resources, the Company commenced a restructuring plan in June 2019 that included reducing staff and suspending development of its inflammasome disease candidate, CTS-2090, and commenced a second restructuring plan in September 2019 that included reducing additional staff to further extend the Company’s resources. The Company engaged a financial advisor to assist in the exploration and evaluation of strategic alternatives to enhance shareholder value, including a merger, an acquisition or sale of assets or a dissolution and liquidation of the Company. On January 28, 2020, Conatus, Chinook Merger Sub, Inc. (Merger Sub), and Histogen Inc. (Histogen) entered into the Agreement and Plan of Merger and Reorganization (Merger Agreement), pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Histogen, with Histogen continuing as Conatus’ wholly owned subsidiary and the surviving corporation of the merger. See Note 14 – Subsequent Events for additional information. As of December 31, 2019, the Company has devoted substantially all of its efforts to product development and has not realized product sales revenues from its planned principal operations. The Company has a limited operating history, and the sales and income potential of the Company’s business and market are unproven. The Company has experienced net losses since its inception and, as of December 31, 2019, had an accumulated deficit of $198.0 million. The Company expects to continue to incur net losses for at least the next several years. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. As of December 31, 2019, the Company had cash and cash equivalents of $20.7 million and working capital of $20.0 million. Based on the Company’s current business plan, management believes that its existing cash and cash equivalents will be sufficient to fund the Company‘s obligations for at least twelve months from the issuance date of these financial statements. If the Company is unable to generate revenues adequate to support its cost structure, the Company may need to raise additional equity or debt financing or seek to complete one of the strategic alternatives described above.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash. Additionally, the Company established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts. Marketable Securities The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the statements of operations and comprehensive loss and as a separate component of stockholders’ equity. The Company classifies marketable securities with remaining maturities greater than one year as current assets because such marketable securities are available to fund the Company’s current operations. The Company invests its excess cash balances primarily in corporate debt securities and money market funds with strong credit ratings. Realized gains and losses are calculated on the specific identification method and recorded as interest income. There were no realized gains and losses for the years ended December 31, 2019, 2018 and 2017. At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security’s relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. When the Company determines that a decline in the fair value below its cost basis is other-than-temporary, the Company recognizes an impairment loss in the period in which the other-than-temporary decline occurred. There have been no other-than-temporary declines in the value of marketable securities for the years ended December 31, 2019, 2018 and 2017. Fair Value of Financial Instruments The carrying amounts of collaboration receivables, prepaid and other current assets, and accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items. Property and Equipment Property and equipment, which consisted of furniture and fixtures, computers and office equipment, scientific equipment and leasehold improvements, were stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements were amortized over the shorter of their estimated useful lives or the lease term. Long-Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objective. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset’s fair value. Through December 31, 2019, the Company has recognized $50,000 in impairment losses. Revenue Recognition Under the relevant accounting literature, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. The Company performs the following five steps in order to determine revenue recognition for contracts: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, the entity satisfies a performance obligation. At contract inception, the Company identifies the performance obligations in the contract by assessing whether the goods or services promised within each contract are distinct. Revenue is then recognized for the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. In a contract with multiple performance obligations, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation, which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price(s) may include estimates regarding forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. Any change made to estimated progress towards completion of a performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in a contract, the Company recognizes revenues from the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from the allocated transaction price. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue or expense recognition as a change in estimate. At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being reached. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or a collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of milestones that are within its or a collaboration partner’s control, such as operational developmental milestones and any related constraint, and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which will affect collaboration revenues and earnings in the period of adjustment. Revisions to the Company’s estimate of the transaction price may also result in negative collaboration revenues and earnings in the period of adjustment. For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, and a license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, the Company has not recognized any royalty revenue from collaborative arrangements. In December 2016, the Company entered into an Option, Collaboration and License Agreement (the Collaboration Agreement) and an Investment Agreement (the Investment Agreement) with Novartis Pharma AG (Novartis). The Company concluded that there were two significant performance obligations under the Collaboration Agreement: the license and the research and development services, but that the license is not distinct from the research and development services as Novartis cannot obtain value from the license without the research and development services, which the Company is uniquely able to perform. The Company concluded that progress towards completion of the performance obligations related to the Collaboration Agreement is best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The Company periodically reviews and updates the estimated collaboration expenses, when appropriate, which adjusts the percentage of revenue that is recognized for the period. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in the period could be materially impacted. The transaction price to be recognized as revenue under the Collaboration Agreement consists of the upfront payment, option exercise fee, deemed revenue from the premium paid by Novartis under the Investment Agreement and estimated reimbursable research and development costs. Certain expenses directly related to execution of the Collaboration Agreement were capitalized as assets on the balance sheet and are being expensed in a manner consistent with the methodology used for recognizing revenue. The Collaboration Agreement was terminated, effective September 30, 2019, and the Company will not receive any future milestone, royalty or profit and loss sharing payments under the Collaboration Agreement. See Note 9 – Collaboration and License Agreements for further information. Research and Development Expenses All research and development costs are expensed as incurred. Income Taxes The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. As of December 31, 2019, there are no unrecognized tax benefits included in the balance sheet that would, if recognized, affect the Company’s effective tax rate. The Company has not recognized interest and penalties in the balance sheets or statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2019, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities. Stock-Based Compensation Stock-based compensation expense for stock option grants and restricted stock units (RSUs) under the Company’s equity plans is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period of the stock-based award, and forfeitures are recognized as they occur. Stock-based compensation expense for employee stock purchases under the Company’s 2013 Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month ESPP offering period. The estimation of fair value for stock-based compensation requires management to make estimates and judgments about, among other things, employee exercise behavior, forfeiture rates and volatility of the Company’s common stock. The judgments directly affect the amount of compensation expense that will be recognized. The fair value of stock options is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method. The expected volatility of stock options is based upon the historical volatility of the Company and a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2019 2018 2017 Assumptions Risk-free interest rate 1.82% - 2.50% 2.55% - 3.03% 1.83% - 2.13% Expected dividend yield 0% 0% 0% Expected volatility 105% - 119% 94% - 100% 93% - 97% Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1 Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from nonowner sources, including unrealized gains and losses on marketable securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is used in making decisions regarding resource allocation and assessing performance. To date, the Company has viewed its operations and managed its business as one segment operating primarily in the United States. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common share equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities have been excluded from the computation of diluted net loss per share in the periods in which they would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to compute basic and diluted shares outstanding due to the Company’s net loss position. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in thousands): December 31, 2019 2018 2017 Warrants to purchase common stock 13 13 150 Common stock options issued and outstanding 1,299 5,385 4,826 RSUs outstanding 1,453 — — Shares issuable upon conversion of convertible note payable — — 2,965 ESPP shares pending issuance — 8 5 Total 2,765 5,406 7,946 Recent Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes, as part of its initiative to reduce complexity in accounting standards. The amendments in the ASU are effective for fiscal years beginning after December 15, 2020, including interim periods therein. Early adoption of the standard is permitted, including adoption in interim or annual periods for which financial statements have not yet been issued. We have not early adopted this ASU for 2019. The ASU is currently not expected to have a material impact on our financial statements. In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842). This guidance requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. ASU 2016-02 establishes a right-of-use model (ROU) that requires a lessee to recognize an ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months. The Company adopted this standard effective January 1, 2019, as required, retrospectively through a cumulative effect adjustment. The new standard provides a number of optional practical expedients in transition. The Company elected the “package of practical expedients,” which permits the Company not to reassess, under ASU 2016-02, prior conclusions about lease identification, lease classification and initial direct costs. The new standard also provides practical expedients for an entity’s ongoing accounting. The Company elected to utilize the short-term lease recognition exemption for all leases that qualify. This means, for those short-term leases that qualify, the Company will not recognize ROU assets or lease liabilities. The Company also elected not to separate lease and non-lease components for facility leases. Adoption of this guidance resulted in the recognition of lease liabilities of $0.7 million, based on the present value of the remaining minimum rental payments under current leasing standards for the Company’s applicable existing office space operating lease, with corresponding ROU assets of $0.6 million. See Note 11 – Commitments for further information.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Includes financial instruments for which quoted market prices for identical instruments are available in active markets. Level 2: Includes financial instruments for which there are inputs other than quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transaction (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data. Level 3: Includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions. Below is a summary of assets, including cash, cash equivalents and marketable securities, measured at fair value as of December 31, 2019 and 2018 (in thousands): Fair Value Measurements Using December 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 1,870 $ 1,870 $ — $ — Money market funds 18,833 18,833 — — Total $ 20,703 $ 20,703 $ — $ — Fair Value Measurements Using December 31, 2018 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 2,072 $ 2,072 $ — $ — Money market funds 8,000 8,000 — — Corporate debt securities 30,620 — 30,620 — Total $ 40,692 $ 10,072 $ 30,620 $ — At December 31, 2018, the Company’s marketable securities, consisting principally of debt securities, are classified as available-for-sale, are stated at fair value, and consist of Level 2 financial instruments in the fair value hierarchy. The Company determines the fair value of its debt security holdings based on pricing from a service provider. The service provider values the securities based on using market prices from a variety of industry-standard independent data providers. Such market prices may be quoted prices in active markets for identical assets (Level 1 inputs) or pricing determined using inputs other than quoted prices that are observable either directly or indirectly (Level 2 inputs), such as yield curve, volatility factors, credit spreads, default rates, loss severity, current market and contractual prices for the underlying instruments or debt, broker and dealer quotes, as well as other relevant economic measures.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities The Company invests its excess cash in money market funds and debt instruments of financial institutions, corporations, government sponsored entities and municipalities. The Company had no investments in marketable securities at December 31, 2019, the following tables summarize the Company’s investments in marketable securities at December 31, 2018 (in thousands): As of December 31, 2018 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 29,144 $ — $ (17 ) $ 29,127 Total $ 29,144 $ — $ (17 ) $ 29,127

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment consist of the following (in thousands): December 31, 2019 2018 Furniture and fixtures $ — $ 334 Equipment — 208 Leasehold improvements — 147 — 689 Less accumulated depreciation and amortization — (535 ) Total $ — $ 154 Depreciation expense related to property and equipment was $73,000, $91,000 and $108,000 for the years ended December 31, 2019, 2018 and 2017, respectively. At December 31, 2019, the Company wrote off the remaining net book value of its property and equipment, which totaled approximately $0.1 million

Notes Payable

Notes Payable	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Notes Payable	6. Notes Payable In July 2010, the Company issued to Pfizer Inc. (Pfizer) a $1.0 million promissory note (the Pfizer Note). The Pfizer Note bore interest at a rate of 7% per annum and was scheduled to mature on July 29, 2020. Interest was payable on a quarterly basis. On January 24, 2017, the Company voluntarily prepaid the entire balance of the outstanding principal and accrued and unpaid interest of the Pfizer Note in the amount of $1,004,861. Prior to the prepayment of the Pfizer Note, the Company recorded the Pfizer Note on the balance sheet at face value. Based on borrowing rates available to the Company for loans with similar terms, the Company believed that the fair value of the Pfizer Note approximated its carrying value. The fair value measurement was categorized within Level 3 of the fair value hierarchy. On February 15, 2017, the Company issued a convertible promissory note (the Novartis Note) in the principal amount of $15.0 million, pursuant to the Investment Agreement. The Novartis Note bore interest on the unpaid principal balance at a rate of 6% per annum and had a scheduled maturity date of December 31, 2019. The terms of the Novartis Note allowed the Company to convert the principal and accrued interest into the Company’s common stock at a conversion price equal to 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date. The ability to borrow and repay the debt at a discount using shares of the Company’s common stock was deemed to be additional, foregone revenue attributable to the Collaboration Agreement, which the Company imputed and recorded as both a receivable from Novartis and a liability (deferred revenue) of $2.5 million at the inception of the Collaboration Agreement and the Investment Agreement. On February 15, 2017, the Company recorded the $15.0 million proceeds from the issuance of the Novartis Note as a convertible note payable in the amount of $12.5 million and a reduction of the outstanding receivable from Novartis of $2.5 million. On December 5, 2018, the Company, at its option, converted the entire outstanding principal of $15.0 million and accrued and unpaid interest of the Novartis Note into 2,882,519 shares of the Company’s common stock at a conversion price of $5.77 per share. The Company elected to account for the Novartis Note under the fair value option. Prior to conversion of the Novartis Note, the Company concluded that the fair value of the Novartis Note remained at $12.5 million, plus the related accrued interest, due to its conversion features. The fair value measurement was categorized within Level 2 of the fair value hierarchy.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity Common Stock In May 2017, the Company completed a public offering of 5,980,000 shares of its common stock at a public offering price of $5.50 per share. The shares were registered pursuant to the Company’s Registration Statement on Form S-3 filed on August 14, 2014. The Company received net proceeds of $30.6 million, after deducting underwriting discounts and commissions and offering-related transaction costs. Immediately following the offering, the Company used $11.2 million of the net proceeds to repurchase and retire 2,166,836 shares of its common stock from funds affiliated with Advent Private Equity (collectively Advent) at a price of $5.17 per share , which is equal to the net proceeds per share that the Company received from the offering, before expenses, pursuant to a stock purchase agreement the Company entered into with Advent in May 2017. On August 2, 2018, the Company entered into an At Market Issuance Sales Agreement (the Sales Agreement) with Stifel, Nicolaus & Company, Incorporated (Stifel), pursuant to which the Company may sell from time to time, at its option, up to an aggregate of $35.0 million of shares of its common stock through Stifel, as sales agent. Sales of the Company’s common stock made pursuant to the Sales Agreement, if any, will be made on The Nasdaq Capital Market (Nasdaq), under the Company’s Registration Statement on Form S-3 filed on August 17, 2017 and declared effective by the SEC on November 9, 2017, by means of ordinary brokers’ transactions at market prices. Additionally, under the terms of the Sales Agreement, the Company may also sell shares of its common stock through Stifel, on Nasdaq or otherwise, at negotiated prices or at prices related to the prevailing market price. The Company will pay a commission rate equal to up to 3.0% of the gross sales price per share sold. As of December 31, 2019, no shares were issued pursuant to the Sales Agreement. Warrants In 2013, the Company issued warrants exercisable for 1,124,026 shares of Series B preferred stock, at an exercise price of $0.90 per share, to certain existing investors in conjunction with a private placement (the 2013 Warrants) and warrants exercisable for 111,112 shares of Series B preferred stock, at an exercise price of $0.90 per share, to Oxford Finance LLC and Silicon Valley Bank in conjunction with the Company’s entry into a loan and security agreement (the Lender Warrants). Upon completion of the Company’s initial public offering (IPO), the 2013 Warrants and the Lender Warrants became exercisable for 136,236 and 13,468 shares of common stock, respectively, at an exercise price of $7.43 per share. The 2013 Warrants expired on May 30, 2018, and the Lender Warrants will expire on July 3, 2023. Stock Options The Company adopted an Equity Incentive Plan in 2006 (the 2006 Plan) under which 1,030,303 shares of common stock were reserved for issuance to employees, nonemployee directors and consultants of the Company. In July 2013, the Company adopted an Incentive Award Plan (the 2013 Plan), which provides for the grant of incentive stock options, nonstatutory stock options, rights to purchase restricted stock, stock appreciation rights, dividend equivalents, stock payments and restricted stock units to eligible recipients. Recipients of incentive stock options shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The maximum term of options granted under the 2013 Plan is ten years. Except for annual grants to non-employee directors, which vest one year from the grant date, options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years. Pursuant to the 2013 Plan, the Company’s management is authorized to grant stock options to the Company’s employees, directors and consultants. The number of shares available for future grant under the 2013 Plan will automatically increase each year by an amount equal to the least of (1) 1,000,000 shares of the Company’s common stock, (2) 5% of the outstanding shares of the Company’s common stock as of the last day of the Company’s immediately preceding fiscal year, or (3) such other amount as the Company’s board of directors may determine. Shares that remain available, that expire or otherwise terminate without having been exercised in full, and unvested shares that are forfeited to or repurchased by the Company under the 2006 Plan will roll into the 2013 Plan. As of December 31, 2019, a total of 3,951,438 options remain available for future grant under the 2013 Plan. On August 31, 2017, in connection with the appointment of its new Executive Vice President, Chief Operating Officer and Chief Financial Officer, the Company granted stock options to purchase 525,000 shares of the Company’s common stock outside of its stock option plans. The following table summarizes the Company’s stock option activity under all stock option plans for the three years ended December 31, 2019 (options in thousands): Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2016 3,394 $ 5.10 Granted 1,733 4.91 Exercised (79 ) 1.32 Forfeited/cancelled/expired (222 ) 6.09 Outstanding at December 31, 2017 4,826 5.05 Granted 943 5.08 Exercised (211 ) 1.71 Forfeited/cancelled/expired (173 ) 4.83 Outstanding at December 31, 2018 5,385 5.20 Granted 1,723 1.84 Exercised — 0.00 Forfeited/cancelled/expired (5,809 ) 4.51 Outstanding at December 31, 2019 1,299 $ 3.82 5.2 Exercisable at December 31, 2019 1,134 $ 4.29 4.5 The weighted-average fair value of options granted for the years ended December 31, 2019, 2018 and 2017 were $1.84, $3.93 and $3.79, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2019, 2018 and 2017 were $0.0 million, $0.6 million and $0.3 million, respectively. At December 31, 2019, the intrinsic value of options outstanding and exercisable were $16,000 and $1,000, respectively. Restricted Stock Units In August 2019, the Company effected a one-time option exchange, wherein certain employees were offered the opportunity to exchange eligible outstanding stock options, whether vested or unvested, with exercise prices that are significantly higher than the current fair market value of the Company’s common stock for the grant of a lesser number of RSUs. The participants received one new RSU for every two stock options tendered for exchange. As a result, 3,200,375 stock options were exchanged for 1,600,186 RSUs. The RSUs have a one-year vesting schedule or vest upon a Change of Control, an employee’s termination without Cause, or resignation for Good Reason, each as defined in the 2013 Incentive Award Plan. The one-time option exchange was accounted for as a modification of the original award, and the difference in the fair value of the cancelled options immediately prior to the cancellation and the fair value of the modified options resulted in incremental value of approximately $0.1 million, which was calculated using the Black-Scholes model. Total stock-based compensation expense to be recognized over the requisite service period is equal to remaining unrecognized expense for the exchanged option, as of the exchange date, plus the incremental value of the modification to the award and is expected to be recorded over the one-year service term commencing August 1, 2019. The following table summarizes the Company’s RSU activity under all equity plans for the three years ended December 31, 2019 (RSUs in thousands): Total RSUs Weighted-Average Grant Date Fair Value per Share Balance at December 31, 2018 — $ — Granted 1,600 0.31 Forfeited (147 ) 0.31 Balance at December 31, 2019 1,453 $ 0.31 Unrecognized compensation expense related to outstanding RSUs at December 31, 2019 was $2.1 million, which is expected to be recognized over a weighted-average vesting term of 0.6 years. Employee Stock Purchase Plan In July 2013, the Company adopted the ESPP, which permits participants to contribute up to 20% of their eligible compensation during defined rolling six-month periods to purchase the Company’s common stock. The purchase price of the shares will be 85% of the lower of the fair market value of the Company’s common stock on the first day of trading of the offering period or on the applicable purchase date. The ESPP was activated in November 2014. The Company issued 5,365, 36,296 and 24,303 shares of common stock under the ESPP for the years ended December 31, 2019, 2018 and 2017, respectively. The Company had an outstanding liability of $0, $28,936 and $16,367 at December 31, 2019, 2018 and 2017, respectively, which is included in accounts payable and accrued expenses on the balance sheets, for employee contributions to the ESPP for shares pending issuance at the end of the offering period. Stock-Based Compensation The Company recorded stock-based compensation of $4.2 million, $3.8 million and $4.1 million for the years ended December 31, 2019, 2018 and 2017, respectively. Unrecognized compensation expense related to outstanding stock options at December 31, 2019 was $27,000, which is expected to be recognized over a weighted-average vesting term of 0.9 years. Common Stock Reserved for Future Issuance The following shares of common stock were reserved for future issuance at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Warrants to purchase common stock 13 13 Common stock options issued and outstanding 1,299 5,385 Common stock authorized for future option grants 3,951 844 RSUs outstanding 1,453 — Common stock authorized for the ESPP 489 495 Total 7,205 6,737

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes Significant components of the Company’s deferred tax assets at December 31, 2019 and 2018 are shown below (in thousands): December 31, 2019 2018 Deferred tax assets Net operating loss carryovers $ 35,901 $ 31,135 Research and development tax credits 8,312 8,641 Intangibles 130 379 Stock options 438 2,255 Compensation 47 452 Deferred revenue — 2,642 Other 88 62 Total gross deferred tax assets 44,916 45,566 Deferred tax liabilities Right-of-use asset 46 — Total net deferred tax assets 44,870 45,566 Less valuation allowance (44,870 ) (45,566 ) Net deferred tax assets $ — $ — A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2019, 2018 and 2017 is as follows: December 31, 2019 2018 2017 Statutory rate 21.0 % 21.0 % 34.0 % Valuation allowance 6.1 % (25.2 )% 51.5 % Federal tax rate change — % — % (93.3 )% General business credits (2.9 )% 6.2 % 10.8 % Expiration of stock options (21.4) % — % — % Other (2.8 )% (2.0 )% (3.0 )% Effective tax rate — % — % — % At December 31, 2019, the Company had federal and state NOL carryforwards of $145.5 million and $76.4 million, respectively. The federal and state NOL carryforwards begin to expire in 2028, unless previously utilized. The federal NOL carryforwards generated after 2017 have an indefinite carryforward life. The Company also has federal, including orphan drug, and state research credit carryforwards of $8.3 million and $2.4 million, respectively. The federal research credit carryforwards will begin expiring in 2027, unless previously utilized. The state research credit will carry forward indefinitely. The change in the valuation allowance is a decrease of $0.7 million for the year ended December 31, 2019, an increase of $4.4 million for the year ended December 31, 2018 and a decrease of $9.0 million for the year ended December 31, 2017. Pursuant to Internal Revenue Code (IRC) Sections 382 and 383, annual use of the Company’s NOL or research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. The Company previously completed a study to assess whether an ownership change, as defined by IRC Section 382, had occurred from its formation through December 31, 2017. Based upon this study, the Company determined that ownership changes had occurred in 2006 and 2013 but The following table summarizes the activity related to the Company’s unrecognized tax benefits (in thousands): 2019 2018 2017 Balance at beginning of year $ 2,221 $ 1,932 $ 1,319 Additions based on tax positions related to the current year — 289 613 Reductions based on tax positions related to prior years (80 ) — — Balance at end of year $ 2,141 $ 2,221 $ 1,932 The Company does not expect that the unrecognized tax benefits will change within 12 months of this reporting date. Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate. The Company’s policy is to recognize interest and penalties related to income tax matters in income tax expense. For the years ended December 31, 2019, 2018 and 2017, the Company has not recognized any interest or penalties related to income taxes. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by the federal and state jurisdictions where applicable. There are currently no pending income tax examinations. The Company’s tax years for 2005 and forward are subject to examination by the federal and California tax authorities due to the carryforward of unutilized net operating losses (NOLs) and research and development credits.

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2019
Collaboration And License Agreements [Abstract]
Collaboration and License Agreements	9. Collaboration and License Agreements In December 2016, the Company entered into the Collaboration Agreement, pursuant to which the Company granted Novartis an exclusive option to collaborate with the Company to develop products containing emricasan. Pursuant to the Collaboration Agreement, the Company received a non-refundable upfront payment of $50.0 million from Novartis. In May 2017, Novartis exercised its option under the Collaboration Agreement. In July 2017, the Company received a $7.0 million option exercise payment, at which time the license under the Collaboration Agreement became effective (the License Effective Date). The Company and Novartis entered into an amendment to the Collaboration Agreement, pursuant to which they mutually agreed to terminate the Collaboration Agreement in September 2019. Under the Collaboration Agreement, the Company was eligible to receive up to an aggregate of $650.0 million in milestone payments over the term of the Collaboration Agreement, contingent on the achievement of certain development, regulatory and commercial milestones, as well as royalties or profit and loss sharing on future product sales in the United States, if any. Novartis was to pay 50% of the Company’s Phase 2b and observational study costs pursuant to an agreed upon budget. Upon completion of the Phase 2b trials, Novartis would have assumed 100% of the observational study costs and full responsibility for emricasan’s Phase 3 development and all combination product development. Due to the termination of the Collaboration Agreement, the Company will not receive any future milestone, royalty or profit and loss sharing payments under the Collaboration Agreement. Pursuant to the terms of termination of the Collaboration Agreement, the Company and Novartis continued to share the costs of the Phase 2b trials equally until December 31, 2019, and Novartis will pay up to $150,000 for its share of the costs of the Phase 2b trials, if any, in 2020. The Company accounted for the termination of the Collaboration Agreement as a contract modification of an existing contract as the remaining services are not distinct and, therefore, form part of a single performance obligation that is partially satisfied as of the contract modification date. Concurrent with entry into the Collaboration Agreement, the Company entered into the Investment Agreement, whereby the Company was able to borrow up to $15.0 million at a rate of 6% per annum, under one or two notes, with a maturity date of December 31, 2019. On February 15, 2017, the Company issued the Novartis Note in the principal amount of $15.0 million pursuant to the Investment Agreement. The terms of the Novartis Note allowed the Company to convert the principal and accrued interest into the Company’s common stock at a conversion price equal to 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date. On December 5, 2018, the Company, at its option, converted the entire outstanding principal of $15.0 million and accrued and unpaid interest of the Novartis Note into 2,882,519 shares of the Company’s common stock at a conversion price of $5.77 per share. Under the Collaboration Agreement, there were two significant performance obligations: the license and the research and development services, but the license was not distinct from the research and development services as Novartis could not obtain value from the license without the research and development services, which the Company was uniquely able to perform. The Company concluded that progress towards completion of the performance obligations related to the Collaboration Agreement was best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The transaction price recognized as revenue under the Collaboration Agreement consisted of the upfront payment, option exercise fee, deemed revenue from the premium paid by Novartis under the Investment Agreement and estimated reimbursable research and development costs. Certain expenses directly related to execution of the Collaboration Agreement were capitalized as assets on the balance sheet and were expensed in a manner consistent with the methodology used for recognizing revenue. During the quarter ended June 30, 2019, as a result of the decision to discontinue the development of emricasan, the Company significantly reduced the transaction price and the total estimated reimbursable research and development expenses under the Collaboration Agreement. The net effect of these changes resulted in the recognition of a cumulative catch-up in revenue of $4.6 million, which was recorded as a change in estimate during the three months ended June 30, 2019. A reconciliation of the opening and closing balances of deferred revenue related to the Collaboration Agreement, which represents the unrecognized balance of the transaction price, is as follows (in thousands): Deferred Revenue Balance at December 31, 2017 $ 26,691 Cumulative effect of adoption of accounting standard 1,299 Additions to deferred revenue 18,486 Revenue recognized (33,586 ) Balance at December 31, 2018 12,890 Additions to deferred revenue 8,826 Revenue recognized (21,716 ) Balance at December 31, 2019 $ — A reconciliation of the opening and closing balances of deferred costs related to execution of the Collaboration Agreement is as follows (in thousands): Deferred Costs Balance at December 31, 2017 $ — Cumulative effect of adoption of accounting standard 687 Costs recognized (377 ) Balance at December 31, 2018 310 Costs recognized (310 ) Balance at December 31, 2019 $ —

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2019
Postemployment Benefits [Abstract]
Employee Benefits	10. Employee Benefits Effective December 4, 2006, the Company has a defined contribution 401(k) plan for its employees. Employees are eligible to participate in the plan beginning on the first day of employment. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation. Effective January 1, 2007,

Commitments

Commitments	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments	11. Commitments Leases The Company determines if an arrangement is a finance lease, operating lease or short-term lease at inception, or as applicable, and accounts for the arrangement under the relevant accounting literature. Currently, the Company is only party to a non-cancelable office space operating lease and short-term lease arrangements. Under the relevant guidance, the Company recognizes operating lease ROU assets and liabilities based on the present value of the future minimum lease payments over the lease term at the commencement date, using the Company’s assumed incremental borrowing rate of 12%, and amortizes the ROU assets and liabilities over the lease term. Lease expense for operating leases is recognized on a straight-line basis over the lease term. The Company’s short-term leases are not subject to recognition of an ROU asset or liability or straight-line lease expense requirements. In February 2014, the Company entered into a noncancelable operating lease agreement (the Lease) for certain office space with a lease term from July 2014 through December 2019 and a renewal option for an additional five years. In May 2015, the Company entered into a first amendment to the Lease (the First Lease Amendment) for additional office space starting in September 2015 through September 2020. The First Lease Amendment also extended the term of the Lease to September 2020. The monthly base rent under the Lease and the First Lease Amendment increases approximately 3% annually from approximately $33,000 in 2015 to approximately $39,000 in 2020. In December 2019, the Company agreed to sublet the office space, in two phases, under the Lease through September 30, 2020, the reminder of the lease term. As the amounts to be received under the sublease agreement were less than the Company’s remaining payment obligations under the Lease, an impairment loss of $50,000 was recorded on the ROU asset, representing the excess of the carrying value of the ROU asset over its fair value. As of December 31, 2019, the Company’s ROU assets and liabilities related to the Lease and the First Lease Amendment are as follows (in thousands): ROU assets (included in other assets) $ 221 Current portion of lease liabilities $ 338 Total lease liabilities $ 338 The following table reconciles the undiscounted cash flows to the operating lease liabilities recorded in the balance sheet as of December 31, 2019 (in thousands): Total lease payments $ 351 Present value adjustment (13) Total lease liabilities $ 338 Rent expense was as follows (in thousands): Year Ended December 31, 2019 2018 2017 Operating lease $ 378 $ 378 $ 378 Short-term leases 68 27 — Total $ 446 $ 405 $ 378 Other Commitments In July 2010, the Company entered into a stock purchase agreement with Pfizer, pursuant to which the Company acquired all of the outstanding stock of Idun Pharmaceuticals, Inc., which was subsequently spun off to the Company’s stockholders in January 2013. Under the stock purchase agreement, the Company may be required to make payments to Pfizer totaling $18.0 million upon the achievement of specified regulatory milestones.

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	12. Quarterly Financial Data (unaudited) The following tables summarize the unaudited quarterly financial data for the last two fiscal years (in thousands, except per share data): 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 7,024 $ 10,791 $ 3,376 $ 526 Total operating expenses 11,974 11,619 6,759 3,371 Total other income 203 172 130 116 Net loss (4,747 ) (656 ) (3,253 ) (2,729 ) Net loss per share, basic and diluted (1) (0.14 ) (0.02 ) (0.10 ) (0.08 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 9,737 $ 8,774 $ 7,666 $ 7,409 Total operating expenses 14,794 13,331 12,324 11,414 Total other income 39 60 69 99 Net loss (5,018 ) (4,497 ) (4,589 ) (3,906 ) Net loss per share, basic and diluted (1) (0.17 ) (0.15 ) (0.15 ) (0.13 ) (1)

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2019
Restructuring And Related Activities [Abstract]
Restructuring Costs	13. Restructuring Costs In June 2019, the Company announced a restructuring plan that included reducing staff and suspending development of its inflammasome disease candidate, CTS-2090, in order to extend the Company’s resources. As a result, during the three months ended June 30, 2019, the Company recognized one-time employee severance expenses of $1.2 million, which were included in accounts payable and accrued expenses on the balance sheet, and noncash stock compensation expenses related to accelerated vesting of certain employee stock options of $0.3 million, both of which were recorded as operating expenses on the statement of operations and comprehensive loss. In September 2019, the Company announced a second restructuring plan that included reducing additional staff. As a result, during the three months ended September 30, 2019, the Company recognized one-time employee severance expenses of $0.9 million, which were included in accounts payable and accrued expenses on the balance sheet, and noncash stock compensation expenses related to accelerated vesting of certain employee stock options of $0.3 million, both of which were recorded as operating expenses on the statement of operations and comprehensive loss. At December 31, 2019, the remaining accrued severance liability totals approximately $0.1 million.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events On January 28, 2020, Conatus, Merger Sub, and Histogen, entered into a Merger Agreement, pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Histogen, with Histogen continuing as Conatus’ wholly owned subsidiary and the surviving corporation of the merger. Consummation of the merger is subject to certain closing conditions, including, among other things, approval by Conatus’ and Histogen’s stockholders. Should the Merger Agreement be terminated prior to consummation, the Merger Agreement contains certain termination rights for both Conatus and Histogen, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $500,000, and in some circumstances reimburse the other party’s expenses up to a maximum of $350,000.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash. Additionally, the Company established guidelines regarding approved investments and maturities of investments, which are designed to maintain safety and liquidity.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking and money market accounts.
Marketable Securities	Marketable Securities The Company classifies its marketable securities as available-for-sale and records such assets at estimated fair value in the balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the statements of operations and comprehensive loss and as a separate component of stockholders’ equity. The Company classifies marketable securities with remaining maturities greater than one year as current assets because such marketable securities are available to fund the Company’s current operations. The Company invests its excess cash balances primarily in corporate debt securities and money market funds with strong credit ratings. Realized gains and losses are calculated on the specific identification method and recorded as interest income. There were no realized gains and losses for the years ended December 31, 2019, 2018 and 2017. At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security’s relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. When the Company determines that a decline in the fair value below its cost basis is other-than-temporary, the Company recognizes an impairment loss in the period in which the other-than-temporary decline occurred. There have been no other-than-temporary declines in the value of marketable securities for the years ended December 31, 2019, 2018 and 2017.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of collaboration receivables, prepaid and other current assets, and accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items.
Property and Equipment	Property and Equipment Property and equipment, which consisted of furniture and fixtures, computers and office equipment, scientific equipment and leasehold improvements, were stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements were amortized over the shorter of their estimated useful lives or the lease term.
Long-Lived Assets	Long-Lived Assets The Company regularly reviews the carrying value and estimated lives of all of its long-lived assets, including property and equipment, to determine whether indicators of impairment may exist which warrant adjustments to carrying values or estimated useful lives. The determinants used for this evaluation include management’s estimate of the asset’s ability to generate positive income from operations and positive cash flow in future periods, as well as the strategic significance of the assets to the Company’s business objective. Should an impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset’s fair value. Through December 31, 2019, the Company has recognized $50,000 in impairment losses.
Revenue Recognition	Revenue Recognition Under the relevant accounting literature, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. The Company performs the following five steps in order to determine revenue recognition for contracts: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when, or as, the entity satisfies a performance obligation. At contract inception, the Company identifies the performance obligations in the contract by assessing whether the goods or services promised within each contract are distinct. Revenue is then recognized for the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. In a contract with multiple performance obligations, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation, which determines how the transaction price is allocated among the performance obligations. The estimation of the stand-alone selling price(s) may include estimates regarding forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. Any change made to estimated progress towards completion of a performance obligation and, therefore, revenue recognized will be recorded as a change in estimate. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in a contract, the Company recognizes revenues from the transaction price allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from the allocated transaction price. The Company evaluates the measure of progress at each reporting period and, if necessary, adjusts the measure of performance and related revenue or expense recognition as a change in estimate. At the inception of each arrangement that includes milestone payments, the Company evaluates whether the milestones are considered probable of being reached. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or a collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of milestones that are within its or a collaboration partner’s control, such as operational developmental milestones and any related constraint, and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which will affect collaboration revenues and earnings in the period of adjustment. Revisions to the Company’s estimate of the transaction price may also result in negative collaboration revenues and earnings in the period of adjustment. For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, and a license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, the Company has not recognized any royalty revenue from collaborative arrangements. In December 2016, the Company entered into an Option, Collaboration and License Agreement (the Collaboration Agreement) and an Investment Agreement (the Investment Agreement) with Novartis Pharma AG (Novartis). The Company concluded that there were two significant performance obligations under the Collaboration Agreement: the license and the research and development services, but that the license is not distinct from the research and development services as Novartis cannot obtain value from the license without the research and development services, which the Company is uniquely able to perform. The Company concluded that progress towards completion of the performance obligations related to the Collaboration Agreement is best measured in an amount proportional to the collaboration expenses incurred and the total estimated collaboration expenses. The Company periodically reviews and updates the estimated collaboration expenses, when appropriate, which adjusts the percentage of revenue that is recognized for the period. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in the period could be materially impacted. The transaction price to be recognized as revenue under the Collaboration Agreement consists of the upfront payment, option exercise fee, deemed revenue from the premium paid by Novartis under the Investment Agreement and estimated reimbursable research and development costs. Certain expenses directly related to execution of the Collaboration Agreement were capitalized as assets on the balance sheet and are being expensed in a manner consistent with the methodology used for recognizing revenue. The Collaboration Agreement was terminated, effective September 30, 2019, and the Company will not receive any future milestone, royalty or profit and loss sharing payments under the Collaboration Agreement. See Note 9 – Collaboration and License Agreements for further information.
Research and Development Expenses	Research and Development Expenses All research and development costs are expensed as incurred.
Income Taxes	Income Taxes The Company’s policy related to accounting for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. For those benefits to be recognized, a tax position must be more likely than not to be sustained upon examination by taxing authorities. As of December 31, 2019, there are no unrecognized tax benefits included in the balance sheet that would, if recognized, affect the Company’s effective tax rate. The Company has not recognized interest and penalties in the balance sheets or statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2019, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense for stock option grants and restricted stock units (RSUs) under the Company’s equity plans is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the requisite service period of the stock-based award, and forfeitures are recognized as they occur. Stock-based compensation expense for employee stock purchases under the Company’s 2013 Employee Stock Purchase Plan (the ESPP) is recorded at the estimated fair value of the purchase as of the plan enrollment date and is recognized as expense on a straight-line basis over the applicable six-month ESPP offering period. The estimation of fair value for stock-based compensation requires management to make estimates and judgments about, among other things, employee exercise behavior, forfeiture rates and volatility of the Company’s common stock. The judgments directly affect the amount of compensation expense that will be recognized. The fair value of stock options is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method. The expected volatility of stock options is based upon the historical volatility of the Company and a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2019 2018 2017 Assumptions Risk-free interest rate 1.82% - 2.50% 2.55% - 3.03% 1.83% - 2.13% Expected dividend yield 0% 0% 0% Expected volatility 105% - 119% 94% - 100% 93% - 97% Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1
Comprehensive Loss	Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from nonowner sources, including unrealized gains and losses on marketable securities. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is used in making decisions regarding resource allocation and assessing performance. To date, the Company has viewed its operations and managed its business as one segment operating primarily in the United States.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and common share equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities have been excluded from the computation of diluted net loss per share in the periods in which they would be anti-dilutive. For all periods presented, there is no difference in the number of shares used to compute basic and diluted shares outstanding due to the Company’s net loss position. The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in thousands): December 31, 2019 2018 2017 Warrants to purchase common stock 13 13 150 Common stock options issued and outstanding 1,299 5,385 4,826 RSUs outstanding 1,453 — — Shares issuable upon conversion of convertible note payable — — 2,965 ESPP shares pending issuance — 8 5 Total 2,765 5,406 7,946
Recent Accounting Pronouncements	Recent Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes, as part of its initiative to reduce complexity in accounting standards. The amendments in the ASU are effective for fiscal years beginning after December 15, 2020, including interim periods therein. Early adoption of the standard is permitted, including adoption in interim or annual periods for which financial statements have not yet been issued. We have not early adopted this ASU for 2019. The ASU is currently not expected to have a material impact on our financial statements. In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842). This guidance requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. ASU 2016-02 establishes a right-of-use model (ROU) that requires a lessee to recognize an ROU asset and lease liability on the balance sheet for all leases with a term longer than 12 months. The Company adopted this standard effective January 1, 2019, as required, retrospectively through a cumulative effect adjustment. The new standard provides a number of optional practical expedients in transition. The Company elected the “package of practical expedients,” which permits the Company not to reassess, under ASU 2016-02, prior conclusions about lease identification, lease classification and initial direct costs. The new standard also provides practical expedients for an entity’s ongoing accounting. The Company elected to utilize the short-term lease recognition exemption for all leases that qualify. This means, for those short-term leases that qualify, the Company will not recognize ROU assets or lease liabilities. The Company also elected not to separate lease and non-lease components for facility leases. Adoption of this guidance resulted in the recognition of lease liabilities of $0.7 million, based on the present value of the remaining minimum rental payments under current leasing standards for the Company’s applicable existing office space operating lease, with corresponding ROU assets of $0.6 million. See Note 11 – Commitments for further information.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Schedule of Black-Scholes Option Pricing Model Assumptions	The fair value of stock options is estimated using the Black-Scholes model with the assumptions noted in the following table. The expected life of stock options is based on the simplified method. The expected volatility of stock options is based upon the historical volatility of the Company and a number of publicly traded companies in similar stages of clinical development. The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date. Year Ended December 31, 2019 2018 2017 Assumptions Risk-free interest rate 1.82% - 2.50% 2.55% - 3.03% 1.83% - 2.13% Expected dividend yield 0% 0% 0% Expected volatility 105% - 119% 94% - 100% 93% - 97% Expected term (in years) 5.5 - 6.1 5.5 - 6.1 5.5 - 6.1
Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because to do so would be anti-dilutive (in thousands): December 31, 2019 2018 2017 Warrants to purchase common stock 13 13 150 Common stock options issued and outstanding 1,299 5,385 4,826 RSUs outstanding 1,453 — — Shares issuable upon conversion of convertible note payable — — 2,965 ESPP shares pending issuance — 8 5 Total 2,765 5,406 7,946

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value	Below is a summary of assets, including cash, cash equivalents and marketable securities, measured at fair value as of December 31, 2019 and 2018 (in thousands): Fair Value Measurements Using December 31, 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 1,870 $ 1,870 $ — $ — Money market funds 18,833 18,833 — — Total $ 20,703 $ 20,703 $ — $ — Fair Value Measurements Using December 31, 2018 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Cash $ 2,072 $ 2,072 $ — $ — Money market funds 8,000 8,000 — — Corporate debt securities 30,620 — 30,620 — Total $ 40,692 $ 10,072 $ 30,620 $ —

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Investments in Marketable Securities	The Company invests its excess cash in money market funds and debt instruments of financial institutions, corporations, government sponsored entities and municipalities. The Company had no investments in marketable securities at December 31, 2019, the following tables summarize the Company’s investments in marketable securities at December 31, 2018 (in thousands): As of December 31, 2018 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 29,144 $ — $ (17 ) $ 29,127 Total $ 29,144 $ — $ (17 ) $ 29,127

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following (in thousands): December 31, 2019 2018 Furniture and fixtures $ — $ 334 Equipment — 208 Leasehold improvements — 147 — 689 Less accumulated depreciation and amortization — (535 ) Total $ — $ 154

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity under all stock option plans for the three years ended December 31, 2019 (options in thousands): Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Outstanding at December 31, 2016 3,394 $ 5.10 Granted 1,733 4.91 Exercised (79 ) 1.32 Forfeited/cancelled/expired (222 ) 6.09 Outstanding at December 31, 2017 4,826 5.05 Granted 943 5.08 Exercised (211 ) 1.71 Forfeited/cancelled/expired (173 ) 4.83 Outstanding at December 31, 2018 5,385 5.20 Granted 1,723 1.84 Exercised — 0.00 Forfeited/cancelled/expired (5,809 ) 4.51 Outstanding at December 31, 2019 1,299 $ 3.82 5.2 Exercisable at December 31, 2019 1,134 $ 4.29 4.5
Summary of RSU Activity	The following table summarizes the Company’s RSU activity under all equity plans for the three years ended December 31, 2019 (RSUs in thousands): Total RSUs Weighted-Average Grant Date Fair Value per Share Balance at December 31, 2018 — $ — Granted 1,600 0.31 Forfeited (147 ) 0.31 Balance at December 31, 2019 1,453 $ 0.31
Summary of Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance at December 31, 2019 and 2018 (in thousands): December 31, 2019 2018 Warrants to purchase common stock 13 13 Common stock options issued and outstanding 1,299 5,385 Common stock authorized for future option grants 3,951 844 RSUs outstanding 1,453 — Common stock authorized for the ESPP 489 495 Total 7,205 6,737

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Components of Company's Deferred Tax Assets	Significant components of the Company’s deferred tax assets at December 31, 2019 and 2018 are shown below (in thousands): December 31, 2019 2018 Deferred tax assets Net operating loss carryovers $ 35,901 $ 31,135 Research and development tax credits 8,312 8,641 Intangibles 130 379 Stock options 438 2,255 Compensation 47 452 Deferred revenue — 2,642 Other 88 62 Total gross deferred tax assets 44,916 45,566 Deferred tax liabilities Right-of-use asset 46 — Total net deferred tax assets 44,870 45,566 Less valuation allowance (44,870 ) (45,566 ) Net deferred tax assets $ — $ —
Reconciliation of Statutory Tax Rates and Effective Tax Rates	A reconciliation of the statutory tax rates and the effective tax rates for the years ended December 31, 2019, 2018 and 2017 is as follows: December 31, 2019 2018 2017 Statutory rate 21.0 % 21.0 % 34.0 % Valuation allowance 6.1 % (25.2 )% 51.5 % Federal tax rate change — % — % (93.3 )% General business credits (2.9 )% 6.2 % 10.8 % Expiration of stock options (21.4) % — % — % Other (2.8 )% (2.0 )% (3.0 )% Effective tax rate — % — % — %
Unrecognized Tax Benefits	The following table summarizes the activity related to the Company’s unrecognized tax benefits (in thousands): 2019 2018 2017 Balance at beginning of year $ 2,221 $ 1,932 $ 1,319 Additions based on tax positions related to the current year — 289 613 Reductions based on tax positions related to prior years (80 ) — — Balance at end of year $ 2,141 $ 2,221 $ 1,932

Collaboration and License Agr_2

Collaboration and License Agreements (Tables)	12 Months Ended
	Dec. 31, 2019
Collaboration And License Agreements [Abstract]
Summary of Reconciliation of Deferred Revenue Related to Collaboration Agreement	A reconciliation of the opening and closing balances of deferred revenue related to the Collaboration Agreement, which represents the unrecognized balance of the transaction price, is as follows (in thousands): Deferred Revenue Balance at December 31, 2017 $ 26,691 Cumulative effect of adoption of accounting standard 1,299 Additions to deferred revenue 18,486 Revenue recognized (33,586 ) Balance at December 31, 2018 12,890 Additions to deferred revenue 8,826 Revenue recognized (21,716 ) Balance at December 31, 2019 $ —
Summary of Reconciliation of Deferred Costs Related To Collaboration Agreement	A reconciliation of the opening and closing balances of deferred costs related to execution of the Collaboration Agreement is as follows (in thousands): Deferred Costs Balance at December 31, 2017 $ — Cumulative effect of adoption of accounting standard 687 Costs recognized (377 ) Balance at December 31, 2018 310 Costs recognized (310 ) Balance at December 31, 2019 $ —

Commitments (Tables)

Commitments (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of ROU Assets and Liabilities Related to Lease and First Lease Amendment	As of December 31, 2019, the Company’s ROU assets and liabilities related to the Lease and the First Lease Amendment are as follows (in thousands): ROU assets (included in other assets) $ 221 Current portion of lease liabilities $ 338 Total lease liabilities $ 338
Schedule of Undiscounted Cash Flows for Operating Lease Liabilities Recorded in Balance Sheet	The following table reconciles the undiscounted cash flows to the operating lease liabilities recorded in the balance sheet as of December 31, 2019 (in thousands): Total lease payments $ 351 Present value adjustment (13) Total lease liabilities $ 338
Schedule of Rent Expense	Rent expense was as follows (in thousands): Year Ended December 31, 2019 2018 2017 Operating lease $ 378 $ 378 $ 378 Short-term leases 68 27 — Total $ 446 $ 405 $ 378

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Data	The following tables summarize the unaudited quarterly financial data for the last two fiscal years (in thousands, except per share data): 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 7,024 $ 10,791 $ 3,376 $ 526 Total operating expenses 11,974 11,619 6,759 3,371 Total other income 203 172 130 116 Net loss (4,747 ) (656 ) (3,253 ) (2,729 ) Net loss per share, basic and diluted (1) (0.14 ) (0.02 ) (0.10 ) (0.08 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenues $ 9,737 $ 8,774 $ 7,666 $ 7,409 Total operating expenses 14,794 13,331 12,324 11,414 Total other income 39 60 69 99 Net loss (5,018 ) (4,497 ) (4,589 ) (3,906 ) Net loss per share, basic and diluted (1) (0.17 ) (0.15 ) (0.15 ) (0.13 ) (1)

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation	Jul. 13, 2005
Accumulated deficit	$ 198,014	$ 186,629
Cash and cash equivalents	20,703	$ 11,565
Working capital	$ 20,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2016PerformanceObligation
Summary Of Significant Accounting Policies [Line Items]
Realized gains and losses on investments	$ 0	$ 0	$ 0
Other-than-temporary declines in value of marketable securities	0	0	0
Impairment losses recognized	$ 50,000
Collaboration and license agreement termination period	Sep. 30, 2019
Unrecognized tax benefits that would, if recognized, affect the Company's effective tax rate	$ 0
Recognized interest or penalties on income tax	$ 0	$ 0	$ 0
Risk-free interest rate basis	The risk-free interest rate is based on the average yield of five- and seven-year U.S. Treasury Bills as of the valuation date.
Number of operating segment | Segment	1
ROU assets	$ 221,000			$ 600,000
Lease liabilities	338,000			$ 700,000
Collaboration Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Unrecognized royalty revenue	$ 0
Collaboration Agreement [Member] | Novartis [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of significant performance obligations | PerformanceObligation					2
Collaboration and license agreement termination period	Sep. 30, 2019
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets	5 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Black-Scholes Option Pricing Model Assumptions (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate - Minimum	1.82%	2.55%	1.83%
Risk-free interest rate - Maximum	2.50%	3.03%	2.13%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility - Minimum	105.00%	94.00%	93.00%
Expected volatility - Maximum	119.00%	100.00%	97.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	2,765	5,406	7,946
ESPP shares pending issuance [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	0	8	5
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	13	13	150
Common stock options issued and outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	1,299	5,385	4,826
RSUs outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	1,453	0	0
Shares issuable upon conversion of convertible note payable [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	0	0	2,965

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 20,703	$ 40,692
Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	1,870	2,072
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	18,833	8,000
Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		30,620
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	20,703	10,072
Level 1 [Member] | Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	1,870	2,072
Level 1 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	18,833	8,000
Level 1 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	30,620
Level 2 [Member] | Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 2 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		30,620
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 [Member] | Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 0	0
Level 3 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value		$ 0

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 0	$ 29,127,000

Marketable Securities - Summary

Marketable Securities - Summary of Investments in Marketable Securities (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 29,144,000
Unrealized Gains		0
Unrealized Losses		(17,000)
Estimated Fair Value	$ 0	29,127,000
Corporate debt securities 1 or less years of maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		29,144,000
Unrealized Gains		0
Unrealized Losses		(17,000)
Estimated Fair Value		$ 29,127,000

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 0	$ 689
Less accumulated depreciation and amortization	0	(535)
Total	0	154
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	0	334
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	0	208
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 0	$ 147

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation	$ 73,000	$ 91,000	$ 108,000
Net book value of property and equipment written off	$ 100,000

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) - USD ($)	Dec. 05, 2018	Feb. 15, 2017	Jan. 24, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 19, 2016	Jul. 31, 2010
Debt Instrument [Line Items]
Proceeds from issuance of convertible note payable					$ 0	$ 0	$ 12,500,000
Conversion of convertible note payable					$ 0	$ 13,729,000	$ 0
Novartis [Member] | Investment Agreement [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate				6.00%
Debt instrument, maturity date				Dec. 31, 2019
Deferred revenue								$ 2,500,000
Promissory note [Member] | Pfizer Inc. [Member]
Debt Instrument [Line Items]
Note payable									$ 1,000,000
Debt instrument, interest rate					7.00%
Debt instrument, maturity date					Jul. 29, 2020
Prepayment of notes payable			$ 1,004,861
Convertible Promissory Note [Member] | Novartis [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		6.00%
Debt instrument, maturity date		Dec. 31, 2019
Promissory note, principal amount		$ 15,000,000
Promissory note conversion, description					The terms of the Novartis Note allowed the Company to convert the principal and accrued interest into the Company’s common stock at a conversion price equal to 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date.
Principal and accrued interest of note to be converted into common stock at conversion price, in percentage		120.00%
Trailing period for average closing price per share of common stock		20 days
Proceeds from issuance of convertible note payable		$ 15,000,000
Convertible note payable		12,500,000
Reduction of outstanding receivable		2,500,000
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	2,882,519
Conversion price	$ 5.77
Fair value of convertible note payable					$ 12,500,000
Convertible Promissory Note [Member] | Novartis [Member] | Investment Agreement [Member]
Debt Instrument [Line Items]
Promissory note, principal amount		$ 15,000,000
Principal and accrued interest of note to be converted into common stock at conversion price, in percentage		120.00%
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	2,882,519
Conversion price	$ 5.77

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Aug. 02, 2018	Aug. 31, 2017	Aug. 31, 2019	May 31, 2017	Jul. 31, 2013	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from the issuance of common stock				$ 30,600,000		$ 0	$ 0	$ 30,610,000
Payment for repurchase of common stock						$ 0	$ 0	$ 11,203,000
Total remaining options available for future grant						3,951,000	844,000
Stock options granted to purchase common stock						1,723,000	943,000	1,733,000
Weighted-average fair value of options granted						$ 1.84	$ 3.93	$ 3.79
Total intrinsic value of stock options exercised						$ 0	$ 600,000	$ 300,000
Intrinsic value of options outstanding						16,000
Intrinsic value of options exercisable						1,000
Unrecognized compensation expense						$ 27,000
Weighted-average vesting term						10 months 24 days
Stock-based compensation						$ 4,200,000	$ 3,800,000	$ 4,100,000
Employment Inducement Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted to purchase common stock		525,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted						1,600,000
Unrecognized compensation expense						$ 2,100,000
Weighted-average vesting term						7 months 6 days
2006 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance to employees, nonemployee directors and consultants						1,030,303
2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance to employees, nonemployee directors and consultants					1,000,000
Stock option plans, maximum term of plan					10 years
Stock option plans, remaining vesting period					3 years
Percentage of outstanding shares of common stock					5.00%
Total remaining options available for future grant						3,951,438
2013 Plan [Member] | Tranche right [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option plans, percentage of options vested					25.00%
One-Time Option Exchange [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exchange description						The participants received one new RSU for every two stock options tendered for exchange.
Number of stock options exchanged			3,200,375
Additional stock compensation expense expected service term			1 year
One-Time Option Exchange [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option plans, remaining vesting period			1 year
Number of shares granted			1,600,186
Incremental value of the modifications			$ 100,000
2013 Warrants [Member] | Convertible promissory notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant expiration date									May 30, 2018
2013 Warrants [Member] | Series B Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrant exercisable to purchase shares									1,124,026
2013 Warrants [Member] | Series B Preferred Stock [Member] | Convertible promissory notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of warrant per share									$ 0.90
Lender Warrants [Member] | Series B convertible preferred stock [Member] | Term Loan One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of warrant per share									$ 0.90
Warrant issued									111,112
Warrant expiration date									Jul. 3, 2023
Sales Agreement with Stifel [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares sold under sales agreement						0
Sales Agreement with Stifel [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, value of shares issued	$ 35,000,000
Percentage of commission of gross sales price per share	3.00%
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued								5,980,000
Common stock issued						5,000	36,000	24,000
Common Stock [Member] | 2013 Warrants [Member] | Convertible promissory notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of warrant per share					$ 7.43
Common Stock [Member] | Lender Warrants [Member] | Convertible promissory notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of warrant per share					$ 7.43
Warrants exercisable					13,468
Common Stock [Member] | Stock Purchase Agreement with Advent [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payment for repurchase of common stock				$ 11,200,000
Shares repurchased and retired under stock purchase agreement				2,166,836
Shares repurchased and retired price per share				$ 5.17
Follow on Offering [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares issued				5,980,000
Common stock, price per share				$ 5.50
Post IPO [Member] | Common Stock [Member] | 2013 Warrants [Member] | Convertible promissory notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Warrants exercisable					136,236
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Lower fair market value of purchase price share					85.00%
Outstanding liability						$ 0	$ 28,936	$ 16,367
Employee Stock Purchase Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan, employees contribution					20.00%
Employee Stock Purchase Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued						5,365	36,296	24,303

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Beginning balance	5,385	4,826	3,394
Number of Options, Granted	1,723	943	1,733
Number of Options, Exercised	0	(211)	(79)
Number of Options, Forfeited/cancelled/expired	(5,809)	(173)	(222)
Number of Options, Ending balance	1,299	5,385	4,826
Number of Options, Exercisable	1,134
Weighted-Average Exercise Price, Beginning balance	$ 5.20	$ 5.05	$ 5.10
Weighted-Average Exercise Price, Granted	1.84	5.08	4.91
Weighted-Average Exercise Price, Exercised	0	1.71	1.32
Weighted-Average Exercise Price, Forfeited/cancelled/expired	4.51	4.83	6.09
Weighted-Average Exercise Price, Ending balance	3.82	$ 5.20	$ 5.05
Weighted-Average Exercise Price, Vested, Exercisable	$ 4.29
Weighted-Average Remaining Contractual Term Outstanding	5 years 2 months 12 days
Weighted-Average Remaining Contractual Term Exercisable	4 years 6 months

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of RSU Activity (Detail) - Restricted Stock Units (RSUs) [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total RSUs, Beginning balance | shares	0
Total RSUs, Granted | shares	1,600
Total RSUs, Forfeited | shares	(147)
Total RSUs, Ending balance | shares	1,453
Weighted-Average Grant Date Fair Value per Share, Beginning balance | $ / shares	$ 0
Weighted-Average Grant Date Fair Value per Share, Granted | $ / shares	0.31
Weighted-Average Grant Date Fair Value per Share, Forfeited | $ / shares	0.31
Weighted-Average Grant Date Fair Value per Share, Ending balance | $ / shares	$ 0.31

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares shares in Thousands	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Warrants to purchase common stock	13	13
Common stock options issued and outstanding	1,299	5,385
Common stock authorized for future option grants	3,951	844
RSUs outstanding	1,453	0
Common stock authorized for the ESPP	489	495
Total	7,205	6,737

Income Taxes - Components of Co

Income Taxes - Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Net operating loss carryovers	$ 35,901	$ 31,135
Research and development tax credits	8,312	8,641
Intangibles	130	379
Stock options	438	2,255
Compensation	47	452
Deferred revenue	0	2,642
Other	88	62
Total gross deferred tax assets	44,916	45,566
Deferred tax liabilities
Right-of-use asset	46	0
Total net deferred tax assets	44,870	45,566
Less valuation allowance	(44,870)	(45,566)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Tax Rates and Effective Tax Rates (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory rate	21.00%	21.00%	34.00%
Valuation allowance	6.10%	(25.20%)	51.50%
Federal tax rate change	0.00%	0.00%	(93.30%)
General business credits	(2.90%)	6.20%	10.80%
Expiration of stock options	(21.40%)	0.00%	0.00%
Other	(2.80%)	(2.00%)	(3.00%)
Effective tax rate	0.00%	0.00%	0.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Research credit carryforwards expiration year	2027
Deferred tax asset, change in valuation allowance amount	$ (700,000)	$ 4,400,000	$ (9,000,000)
Cumulative change in ownership percentage	50.00%
Period for cumulative change in ownership percentage	3 years
Minimum percentage of likelihood for uncertain tax position to be recognized	50.00%
Recognized interest or penalties on income tax	$ 0	$ 0	$ 0
Federal and State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	145,500,000
Research credit carryforwards	$ 8,300,000
Operating loss carryforwards expiration year	2028
State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 76,400,000
Research credit carryforwards	$ 2,400,000

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 2,221	$ 1,932	$ 1,319
Additions based on tax positions related to the current year	0	289	613
Reductions based on tax positions related to prior years	(80)	0	0
Balance at end of year	$ 2,141	$ 2,221	$ 1,932

Collaboration and License Agr_3

Collaboration and License Agreements - Additional Information (Detail) - USD ($)	Dec. 05, 2018	Feb. 15, 2017	Dec. 31, 2016	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2020	Jul. 05, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license agreement termination period					Sep. 30, 2019
Conversion of convertible note payable					$ 0	$ 13,729,000	$ 0
Cumulative catch-up adjustment in revenue				$ 4,600,000
Novartis [Member] | Convertible Promissory Note [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Debt instrument, interest rate		6.00%
Debt instrument, maturity date		Dec. 31, 2019
Debt instrument, conversion price percentage		120.00%
Promissory note, principal amount		$ 15,000,000
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	2,882,519
Conversion price	$ 5.77
Collaboration Agreement [Member] | Novartis [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable payment received			$ 50,000,000
Proceeds from option exercised									$ 7,000,000
Collaboration and license agreement termination period					Sep. 30, 2019
Maximum milestone payments to be received upon achievement of certain milestones			$ 650,000,000
Percentage of observational study costs			50.00%
Assumed percentage of observational study costs upon completion of ongoing Phase 2b trails			100.00%
Collaboration Agreement [Member] | Novartis [Member] | Scenario Forecast [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments								$ 150,000,000
Investment Agreement [Member] | Novartis [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Debt instrument, maximum borrowing capacity			$ 15,000,000
Debt instrument, interest rate			6.00%
Debt instrument, maturity date			Dec. 31, 2019
Investment Agreement [Member] | Novartis [Member] | Convertible Promissory Note [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Debt instrument, conversion price percentage		120.00%
Number of days trailing average closing price of common stock immediately prior to the conversion date		20 days
Promissory note, principal amount		$ 15,000,000
Conversion of convertible note payable	$ 15,000,000
Conversion of convertible note payable to common stock	2,882,519
Conversion price	$ 5.77

Collaboration and License Agr_4

Collaboration and License Agreements - Summary of Reconciliation of Deferred Revenue Related to Collaboration Agreement (Detail) - Collaboration Agreement [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance	$ 12,890	$ 26,691
Cumulative effect of adoption of accounting standard		1,299
Additions to deferred revenue	8,826	18,486
Revenue recognized	(21,716)	(33,586)
Balance	$ 0	$ 12,890

Collaboration and License Agr_5

Collaboration and License Agreements - Summary of Reconciliation of Deferred Costs Related To Collaboration Agreement (Detail) - Collaboration Agreement [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance	$ 310	$ 0
Cumulative effect of adoption of accounting standard		687
Costs recognized	(310)	(377)
Balance	$ 0	$ 310

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postemployment Benefits [Abstract]
Defined contribution plan, Employees voluntary contributions, Amount	$ 192,000	$ 239,000	$ 217,000
Eligibility criteria for employees to participate in the plan	Employees are eligible to participate in the plan beginning on the first day of employment.

Commitments - Additional Inform

Commitments - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2010
Operating Leased Assets [Line Items]
Incremental borrowing rate		12.00%
ROU asset, impairment loss		$ 50,000	$ 0	$ 0
Amount payable upon the achievement of specified regulatory milestone					$ 18,000,000
Operating lease term July 2014 through December 2019 [Member]
Operating Leased Assets [Line Items]
Lease renewal term		5 years
Operating lease term September 2015 through September 2020 [Member]
Operating Leased Assets [Line Items]
Percentage of base rent escalator	3.00%
Rent expense	$ 33,000
Lease agreement rent expense for future period	$ 39,000
ROU asset, impairment loss		$ 50,000

Commitments - Schedule of ROU A

Commitments - Schedule of ROU Assets and Liabilities Related to Lease and First Lease Amendment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
ROU assets	$ 221	$ 600
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Current portion of lease liabilities	$ 338		$ 0
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OperatingLeaseLiabilityCurrent
Total lease liabilities	$ 338	$ 700

Commitments - Schedule of Undis

Commitments - Schedule of Undiscounted Cash Flows for Operating Lease Liabilities Recorded in Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Commitments And Contingencies Disclosure [Abstract]
Total lease payments	$ 351
Present value adjustment	(13)
Lease liabilities	$ 338	$ 700

Commitments - Schedule of Rent

Commitments - Schedule of Rent Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Operating lease	$ 378	$ 378	$ 378
Short-term leases	68	27	0
Total	$ 446	$ 405	$ 378

Quarterly Financial Data - Summ

Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 526		$ 3,376		$ 10,791		$ 7,024		$ 7,409		$ 7,666		$ 8,774		$ 9,737		$ 21,717	$ 33,586	$ 35,377
Total operating expenses	3,371		6,759		11,619		11,974		11,414		12,324		13,331		14,794		33,723	51,863	52,927
Total other income	116		130		172		203		99		69		60		39		621	267	154
Net loss	$ (2,729)		$ (3,253)		$ (656)		$ (4,747)		$ (3,906)		$ (4,589)		$ (4,497)		$ (5,018)		$ (11,385)	$ (18,010)	$ (17,396)
Net loss per share, basic and diluted	$ (0.08)	[1]	$ (0.10)	[1]	$ (0.02)	[1]	$ (0.14)	[1]	$ (0.13)	[1]	$ (0.15)	[1]	$ (0.15)	[1]	$ (0.17)	[1]	$ (0.34)	$ (0.59)	$ (0.61)
[1]	Net loss per share is computed independently for each quarter and the full year based upon respective shares outstanding; therefore, the sum of the quarterly net loss per share amounts may not equal the annual amounts reported.

Restructuring Costs - Additiona

Restructuring Costs - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Accrued severance liability			$ 0.1
Employee Severance [Member] | Operating Expense [Member]
Restructuring Cost And Reserve [Line Items]
Severance expenses	$ 0.9	$ 1.2
Stock Compensation Expense [Member] | Operating Expense [Member]
Restructuring Cost And Reserve [Line Items]
Increase in noncash stock compensation expenses	$ 0.3	$ 0.3

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Events [Member] - Merger Agreement [Member]	Jan. 28, 2020USD ($)
Subsequent Event [Line Items]
Termination fee	$ 500,000
Maximum [Member]
Subsequent Event [Line Items]
Reimburse the other party’s expenses	$ 350,000