Histogen (HSTO) 10-Q 5 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	May 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Trading Symbol	CNAT
Entity Registrant Name	Conatus Pharmaceuticals Inc.
Entity Central Index Key	1,383,701
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		26,169,896

Condensed Balance Sheets

Condensed Balance Sheets - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 16,475,482	$ 58,083,409
Marketable securities	64,065,876	18,931,715
Other receivables		2,500,000
Prepaid and other current assets	889,862	937,436
Total current assets	81,431,220	80,452,560
Property and equipment, net	237,775	261,446
Other assets	1,884,993	1,609,834
Total assets	83,553,988	82,323,840
Current liabilities:
Accounts payable and accrued expenses	5,697,714	5,311,093
Accrued compensation	938,735	2,351,703
Current portion of deferred revenue	27,449,116	30,897,192
Note payable		1,000,000
Total current liabilities	34,085,565	39,559,988
Deferred revenue, less current portion	17,253,762	20,803,762
Convertible note payable	12,592,466
Deferred rent	161,451	171,544
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000,000 shares authorized; 26,169,896 shares issued and outstanding at March 31, 2017; 26,118,722 shares issued and outstanding at December 31, 2016	2,617	2,612
Additional paid-in capital	173,710,486	172,424,531
Accumulated other comprehensive loss	(19,162)	(6,145)
Accumulated deficit	(154,233,197)	(150,632,452)
Total stockholders’ equity	19,460,744	21,788,546
Total liabilities and stockholders’ equity	$ 83,553,988	$ 82,323,840

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
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	26,169,896	26,118,722
Common stock, shares outstanding	26,169,896	26,118,722

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues:
Collaboration revenue	$ 6,998,076
Total revenues	6,998,076
Operating expenses:
Research and development	7,925,711	$ 4,698,462
General and administrative	2,763,025	2,576,127
Total operating expenses	10,688,736	7,274,589
Loss from operations	(3,690,660)	(7,274,589)
Other income (expense):
Interest income	170,841	26,978
Interest expense	(97,327)	(17,500)
Other expense	(5,599)	(6,773)
Total other income	67,915	2,705
Net loss	(3,622,745)	(7,271,884)
Other comprehensive income (loss):
Net unrealized (losses) gains on marketable securities	(13,017)	9,643
Comprehensive loss	$ (3,635,762)	$ (7,262,241)
Net loss per share, basic and diluted	$ (0.14)	$ (0.35)
Weighted average shares outstanding used in computing net loss per share, basic and diluted	26,162,958	20,626,044

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net loss	$ (3,622,745)	$ (7,271,884)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	26,089	26,725
Stock-based compensation expense	1,249,473	901,924
Amortization of premium on marketable securities	7,335	22,122
Accrued interest included in convertible note payable	92,466
Changes in operating assets and liabilities:
Other receivables	2,500,000
Prepaid and other current assets	(8,691)	224,354
Other assets	(203,094)
Accounts payable and accrued expenses	367,652	(252,818)
Accrued compensation	(1,412,968)	(544,584)
Deferred revenue	(6,998,076)
Deferred rent	(6,924)	(3,850)
Net cash used in operating activities	(8,009,483)	(6,898,011)
Investing activities
Maturities of marketable securities	8,994,000	13,875,000
Purchase of marketable securities	(54,148,513)	(4,240,142)
Capital expenditures	(2,418)	(105,114)
Net cash (used in) provided by investing activities	(45,156,931)	9,529,744
Financing activities
Proceeds from issuance of convertible promissory note, net	12,500,000
Principal payment on promissory note	(1,000,000)
Proceeds from issuance of common stock, net		3,076,709
Proceeds from stock issuances under employee stock purchase plan and exercise of stock options	58,487	1,503
Net cash provided by financing activities	11,558,487	3,078,212
Net (decrease) increase in cash and cash equivalents	(41,607,927)	5,709,945
Cash and cash equivalents at beginning of period	58,083,409	13,876,090
Cash and cash equivalents at end of period	16,475,482	19,586,035
Supplemental disclosure of cash flow information:
Cash paid for interest	$ 4,861	$ 17,500

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2017
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 focused on the development and commercialization of novel medicines to treat liver disease. As of March 31, 2017, 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 March 31, 2017, had an accumulated deficit of $154.2 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. 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. The accompanying unaudited interim condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the Securities and Exchange Commission (SEC) related to a quarterly report on Form 10-Q. Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. The unaudited interim condensed financial statements reflect all adjustments which, in the opinion of management, are necessary for a fair statement of the results for the periods presented. All such adjustments are of a normal and recurring nature. The operating results presented in these unaudited interim condensed financial statements are not necessarily indicative of the results that may be expected for any future periods. These unaudited interim condensed financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2016 included in the Company’s annual report on Form 10-K filed with the SEC on March 16, 2017.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of condensed financial statements in conformity with 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 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 condensed balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the condensed 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 three-month periods ended March 31, 2017 and 2016. 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, as it is more likely than not the Company will hold the securities until maturity or a recovery of the cost basis. Fair Value of Financial Instruments The carrying amounts of prepaid and other current assets, accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items. Stock-Based Compensation Stock-based compensation expense for stock option grants under the Company’s stock option 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. 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 stock option and ESPP fair value 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. Property and Equipment Property and equipment, which consists of furniture and fixtures, computers and office equipment and leasehold improvements, are stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements are 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. The Company has not recognized any impairment losses through March 31, 2017. Revenue Recognition The Company recognizes revenue when each of the following four criteria is met: (i) persuasive evidence of an arrangement exists; (ii) products are delivered or as services are rendered; (iii) the sales price is fixed or determinable; and (iv) collectability is reasonably assured. The Company recognizes revenue under its Option, Collaboration and License Agreement (the Collaboration Agreement) with Novartis Pharma AG (Novartis) based on the relevant accounting literature. Under this guidance, multiple elements or deliverables may include (i) grants of licenses, or options to obtain licenses, to intellectual property, (ii) research and development services, (iii) participation on joint research and/or joint development committees, and/or (iv) manufacturing or supply services. The payments entities may receive under these arrangements typically include one or more of the following: non-refundable, upfront license fees; option exercise fees; funding of research and/or development efforts; amounts due upon the achievement of specified objectives; and/or royalties on future product sales. Multiple-element arrangements require the separability of deliverables included in an arrangement into different units of accounting and the allocation of arrangement consideration to the units of accounting. The evaluation of multiple-element arrangements requires management to make judgments about (i) the identification of deliverables, (ii) whether such deliverables are separable from the other aspects of the contractual relationship, (iii) the estimated selling price of each deliverable, and (iv) the expected period of performance for each deliverable. To determine the units of accounting under a multiple-element arrangement, management evaluates certain separation criteria, including whether the deliverables have stand-alone value, based on the relevant facts and circumstances for each arrangement. Management then estimates the selling price for each unit of accounting and allocates the arrangement consideration to each unit using the relative selling price method. The allocated consideration for each unit of accounting is recognized based on the method most appropriate for that unit of account and in accordance with the revenue recognition criteria detailed above. If there are deliverables in an arrangement that are not separable from other aspects of the contractual relationship, they are treated as a combined unit of accounting, with the allocated revenue for the combined unit recognized in a manner consistent with the revenue recognition applicable to the final deliverable in the combined unit. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets and recognized as revenue when the related revenue recognition criteria are met. The Collaboration Agreement provides for non-refundable milestone payments. The Company recognizes revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to the Company for such milestone (i) is consistent with the Company’s performance necessary to achieve the milestone or the increase in value to the collaboration resulting from the Company’s performance, (ii) relates solely to the Company’s past performance and (iii) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, the Company considers all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. The Company periodically reviews the estimated performance periods under the Collaboration Agreement, which provides for non-refundable upfront payments and fees. The Company will adjust the periods over which revenue should be recognized when appropriate to reflect changes in assumptions relating to the estimated performance periods. The Company could accelerate revenue recognition in the event of early termination of programs or if the Company’s expectations change. Alternatively, the Company could decelerate revenue recognition if programs are extended or delayed. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in future periods could be materially impacted. The Company records revenues related to the reimbursement of costs incurred under the Collaboration Agreement where the Company acts as a principal, controls the research and development activities and bears credit risk. Under the Collaboration Agreement, the Company is reimbursed for associated out-of-pocket costs and for a certain amount of the Company’s full-time equivalent (FTE) costs based on an agreed-upon FTE rate. The gross amount of these pass-through reimbursed costs is reported as revenue in the accompanying statements of operations and comprehensive loss, while the actual expenses for which the Company is reimbursed are reflected as research and development costs. See Note 8 – 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, 2016, there are no unrecognized tax benefits included in the condensed balance sheet that would, if recognized, affect the Company’s effective tax rate, and the Company has noted no material changes through March 31, 2017. The Company has not recognized interest and penalties in the condensed balance sheets or condensed statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2016, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities. Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the condensed 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 condensed 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, which include warrants to purchase common stock, outstanding stock options under the Company’s stock option plans, shares issuable upon conversion of convertible note payable, common stock subject to repurchase by the Company and potential shares to be purchased under the ESPP, 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. March 31, 2017 2016 Warrants to purchase common stock 149,704 149,704 Common stock options issued and outstanding 4,175,635 3,309,993 Shares issuable upon conversion of convertible note payable 2,626,713 — Common stock subject to repurchase — 23,053 ESPP shares pending issuance 7,975 15,302 Total 6,960,027 3,498,052 Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606). In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718). In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
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 measured at fair value as of March 31, 2017 and December 31, 2016. Fair Value Measurements Using March 31, 2017 Quoted Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 9,631,826 $ 9,631,826 $ — $ — Corporate debt securities 68,119,220 — 68,119,220 — Total $ 77,751,046 $ 9,631,826 $ 68,119,220 $ — Fair Value Measurements Using December 31, 2016 Quoted Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 45,523,208 $ 45,523,208 $ — $ — Corporate debt securities 27,702,317 — 27,702,317 — Total $ 73,225,525 $ 45,523,208 $ 27,702,317 $ — 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	3 Months Ended
	Mar. 31, 2017
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 following tables summarize the Company’s marketable securities: As of March 31, 2017 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 63,638,149 $ 2,411 $ (22,124 ) $ 63,618,436 Corporate debt securities 1 - 2 446,889 551 — 447,440 Total $ 64,085,038 $ 2,962 $ (22,124 ) $ 64,065,876 As of December 31, 2016 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715 Total $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715

Property and Equipment

Property and Equipment	3 Months Ended
	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment consist of the following: March 31, December 31, 2017 2016 Furniture and fixtures $ 333,670 $ 333,670 Computer equipment and office equipment 121,772 119,354 Leasehold improvements 152,217 152,217 607,659 605,241 Less accumulated depreciation and amortization (369,884 ) (343,795 ) Total $ 237,775 $ 261,446

Note Payable

Note Payable	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Note Payable	6. Note 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. In July 2013, the Pfizer Note was amended to become convertible into shares of the Company’s common stock following the completion of the Company’s initial public offering (IPO), at the option of the holder, at a price per share equal to the fair market value of the common stock on the date of conversion. 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 entered into between the Company and Novartis on December 19, 2016 (the Investment Agreement). The Novartis Note bears interest on the unpaid principal balance at a rate of 6% per annum and has a scheduled maturity date of December 31, 2019. The Company may prepay or convert all or part of the Novartis Note into shares of the Company’s common stock, at its option, until December 31, 2019. Novartis has the option to convert all or part of the Novartis Note into shares of the Company’s common stock upon a change in control of the Company or termination of the Collaboration Agreement by Novartis pursuant to certain provisions. If converted, the principal and accrued interest under the Novartis Note will convert 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. In the event the aggregate number of shares of common stock issued upon the conversion would exceed the lesser of 19.0% of the Company’s outstanding shares on a fully-diluted basis (i) at the inception of the Investment Agreement or (ii) on the conversion date, then only the lesser amount shall convert into shares of common stock and Novartis shall be repaid in cash for any remaining principal and unpaid interest after such conversion. Upon the occurrence of certain events of default, the Novartis Note requires the Company to repay the principal balance of the Novartis Note and any unpaid accrued interest. 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. The convertible note payable, along with the related accrued interest, totaled $12.6 million as of March 31, 2017. The Company elected to account for the Novartis Note under the fair value option. At March 31, 2017, the Company concluded that the fair value of the Novartis Note remained at $12.6 million due to its conversion features. The fair value measurement is categorized within Level 3 of the fair value hierarchy.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity 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 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 and the Lender Warrants will expire on May 30, 2018 and July 3, 2023, respectively. Stock Options The following table summarizes the Company’s stock option activity under all stock option plans for the three months ended March 31, 2017: Total Options Weighted- Average Exercise Price Balance at December 31, 2016 3,393,813 $ 5.10 Granted 888,100 4.31 Exercised (51,174 ) 1.14 Cancelled (55,104 ) 4.42 Balance at March 31, 2017 4,175,635 $ 5.00 Stock-Based Compensation The Company recorded stock-based compensation of $1.2 million and $0.9 million for the three months ended March 31, 2017 and 2016, respectively. Common Stock Reserved for Future Issuance The following shares of common stock were reserved for future issuance at March 31, 2017: Warrants to purchase common stock 149,704 Common stock options issued and outstanding 4,175,635 Common stock authorized for future option grants 767,195 Common stock authorized for the ESPP 555,210 Shares issuable upon conversion of convertible note payable 2,626,713 Total 8,274,457

Collaboration and License Agree

Collaboration and License Agreements	3 Months Ended
	Mar. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration and License Agreements	8. Collaboration and License Agreements In December 2016, the Company entered into the Collaboration Agreement with Novartis, 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, and the Company is due to receive $7.0 million, subject to certain usual and customary closing conditions, including required anti-trust approvals, at which time the license under the Collaboration Agreement will become effective. Under the Collaboration Agreement, the Company will be 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. Pursuant to the Collaboration Agreement, the Company is responsible for completing its Phase 2b trials. In the event the Phase 2b development costs between the execution date of the Collaboration Agreement and the license effective date differ from the budget agreed upon by the parties , Novartis will reimburse the Company for any additional costs, or the Company will credit any amount under budget to Novartis for future reimbursable costs. After the license grant is effective, unless terminated earlier, the Collaboration Agreement will remain in effect on a product-by-product and country-by-country basis until Novartis’ royalty obligations expire. Novartis has certain termination rights in the event of a mandated clinical trial hold for any product containing emricasan as its sole active ingredient. Additionally, after the license effective date, Novartis has the right to terminate the Collaboration Agreement without cause upon 180 days prior written notice to the Company. In such event, the license granted to Novartis will be terminated and revert to the Company. In the event Novartis terminates the Collaboration Agreement due to the Company’s uncured material breach or insolvency, the license granted to Novartis pursuant to the Collaboration Agreement will become irrevocable, and Novartis will be required to continue to make all milestone and royalty payments otherwise due to the Company under the Collaboration Agreement, provided that if the Company materially breaches the Collaboration Agreement such that the rights licensed to Novartis or the commercial prospects of the emricasan products are seriously impaired, the milestone and royalty payments will be reduced by 50%. Under the relevant accounting literature, the Collaboration Agreement meets the definition of a collaborative arrangement and a multiple-element arrangement. The Company concluded that there were two significant deliverables under the Collaboration Agreement – the option to obtain the license and the research and development services – but that the license does not have stand-alone value as Novartis cannot obtain value from the license without the research and development services, which the Company is uniquely able to perform. As such, the Company will recognize as collaboration revenue a portion of the upfront payment received of $50.0 million, the option exercise fee of $7.0 million, and the imputed income from the Investment Agreement as described below on a straight-line basis between the inception of the agreement (or upon exercise with respect to the option exercise fee) through mid 2019 – the estimated period over which the Company expects to perform the research and development services. Due to the inherently unpredictable nature of product development activities, the Company periodically reviews the performance period of the research and development services and will adjust the period over which revenue is recognized when appropriate. The Company could accelerate revenue recognition in the event of early termination of programs or if the Company’s expectations change. Alternatively, the Company could decelerate revenue recognition if programs are extended or delayed. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in future periods could be materially impacted. Expense reimbursements for the Company’s Phase 2b emricasan development costs will be recognized as collaboration revenue when the related expenses are incurred. Under the Investment Agreement, the Company is able to borrow up to $15.0 million at a rate of 6% per annum, under one or two notes, which will mature on December 31, 2019. The Company may elect at its sole discretion to convert all or part of the outstanding principal and accrued interest into fully paid shares of common stock, at 120% of the 20-day trailing average closing price per share of the common stock immediately prior to the conversion date. Novartis has the option to convert all or part of the note(s) into shares of the Company’s common stock upon a change in control of the Company or termination of the Collaboration Agreement by Novartis pursuant to certain provisions. In the event the conversion of the notes would exceed the lesser of 19.0% of the Company’s outstanding shares on a fully-diluted basis (i) at the inception of the Investment Agreement or (ii) on the conversion date, then only the lesser amount shall convert into shares of common stock and Novartis shall be repaid in cash for any remaining principal and unpaid interest after such conversion. This 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 issued the Novartis Note in the principal amount of $15.0 million and recorded the $15.0 million proceeds 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.

Commitments

Commitments	3 Months Ended
	Mar. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments	9 . Commitments 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 $32,784 in 2015 to $39,268 in 2020. Future minimum payments under this noncancelable operating lease total $1.5 million at March 31, 2017. Rent expense was $94,501 for each of the three-month periods ended March 31, 2017 and 2016. 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.

Summary of Significant Accoun15

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of condensed financial statements in conformity with 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 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 condensed balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the condensed 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 three-month periods ended March 31, 2017 and 2016. 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, as it is more likely than not the Company will hold the securities until maturity or a recovery of the cost basis.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of prepaid and other current assets, accounts payable and accrued expenses are reasonable estimates of their fair value because of the short maturity of these items.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense for stock option grants under the Company’s stock option 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. 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 stock option and ESPP fair value 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.
Property and Equipment	Property and Equipment Property and equipment, which consists of furniture and fixtures, computers and office equipment and leasehold improvements, are stated at cost and depreciated over the estimated useful lives of the assets (three to five years) using the straight-line method. Leasehold improvements are 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. The Company has not recognized any impairment losses through March 31, 2017.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when each of the following four criteria is met: (i) persuasive evidence of an arrangement exists; (ii) products are delivered or as services are rendered; (iii) the sales price is fixed or determinable; and (iv) collectability is reasonably assured. The Company recognizes revenue under its Option, Collaboration and License Agreement (the Collaboration Agreement) with Novartis Pharma AG (Novartis) based on the relevant accounting literature. Under this guidance, multiple elements or deliverables may include (i) grants of licenses, or options to obtain licenses, to intellectual property, (ii) research and development services, (iii) participation on joint research and/or joint development committees, and/or (iv) manufacturing or supply services. The payments entities may receive under these arrangements typically include one or more of the following: non-refundable, upfront license fees; option exercise fees; funding of research and/or development efforts; amounts due upon the achievement of specified objectives; and/or royalties on future product sales. Multiple-element arrangements require the separability of deliverables included in an arrangement into different units of accounting and the allocation of arrangement consideration to the units of accounting. The evaluation of multiple-element arrangements requires management to make judgments about (i) the identification of deliverables, (ii) whether such deliverables are separable from the other aspects of the contractual relationship, (iii) the estimated selling price of each deliverable, and (iv) the expected period of performance for each deliverable. To determine the units of accounting under a multiple-element arrangement, management evaluates certain separation criteria, including whether the deliverables have stand-alone value, based on the relevant facts and circumstances for each arrangement. Management then estimates the selling price for each unit of accounting and allocates the arrangement consideration to each unit using the relative selling price method. The allocated consideration for each unit of accounting is recognized based on the method most appropriate for that unit of account and in accordance with the revenue recognition criteria detailed above. If there are deliverables in an arrangement that are not separable from other aspects of the contractual relationship, they are treated as a combined unit of accounting, with the allocated revenue for the combined unit recognized in a manner consistent with the revenue recognition applicable to the final deliverable in the combined unit. Payments received prior to satisfying the relevant revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets and recognized as revenue when the related revenue recognition criteria are met. The Collaboration Agreement provides for non-refundable milestone payments. The Company recognizes revenue that is contingent upon the achievement of a substantive milestone in its entirety in the period in which the milestone is achieved. A milestone is considered substantive when the consideration payable to the Company for such milestone (i) is consistent with the Company’s performance necessary to achieve the milestone or the increase in value to the collaboration resulting from the Company’s performance, (ii) relates solely to the Company’s past performance and (iii) is reasonable relative to all of the other deliverables and payments within the arrangement. In making this assessment, the Company considers all facts and circumstances relevant to the arrangement, including factors such as the scientific, regulatory, commercial and other risks that must be overcome to achieve the milestone, the level of effort and investment required to achieve the milestone and whether any portion of the milestone consideration is related to future performance or deliverables. The Company periodically reviews the estimated performance periods under the Collaboration Agreement, which provides for non-refundable upfront payments and fees. The Company will adjust the periods over which revenue should be recognized when appropriate to reflect changes in assumptions relating to the estimated performance periods. The Company could accelerate revenue recognition in the event of early termination of programs or if the Company’s expectations change. Alternatively, the Company could decelerate revenue recognition if programs are extended or delayed. While such changes to the Company’s estimates have no impact on the Company’s reported cash flows, the amount of revenue recorded in future periods could be materially impacted. The Company records revenues related to the reimbursement of costs incurred under the Collaboration Agreement where the Company acts as a principal, controls the research and development activities and bears credit risk. Under the Collaboration Agreement, the Company is reimbursed for associated out-of-pocket costs and for a certain amount of the Company’s full-time equivalent (FTE) costs based on an agreed-upon FTE rate. The gross amount of these pass-through reimbursed costs is reported as revenue in the accompanying statements of operations and comprehensive loss, while the actual expenses for which the Company is reimbursed are reflected as research and development costs. See Note 8 – 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, 2016, there are no unrecognized tax benefits included in the condensed balance sheet that would, if recognized, affect the Company’s effective tax rate, and the Company has noted no material changes through March 31, 2017. The Company has not recognized interest and penalties in the condensed balance sheets or condensed statements of operations and comprehensive loss. The Company is subject to U.S. and California taxation. As of December 31, 2016, the Company’s tax years beginning 2005 to date are subject to examination by taxing authorities.
Comprehensive Loss	Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the condensed 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 condensed 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, which include warrants to purchase common stock, outstanding stock options under the Company’s stock option plans, shares issuable upon conversion of convertible note payable, common stock subject to repurchase by the Company and potential shares to be purchased under the ESPP, 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. March 31, 2017 2016 Warrants to purchase common stock 149,704 149,704 Common stock options issued and outstanding 4,175,635 3,309,993 Shares issuable upon conversion of convertible note payable 2,626,713 — Common stock subject to repurchase — 23,053 ESPP shares pending issuance 7,975 15,302 Total 6,960,027 3,498,052
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers (Topic 606). In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718). In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments

Summary of Significant Accoun16

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
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. March 31, 2017 2016 Warrants to purchase common stock 149,704 149,704 Common stock options issued and outstanding 4,175,635 3,309,993 Shares issuable upon conversion of convertible note payable 2,626,713 — Common stock subject to repurchase — 23,053 ESPP shares pending issuance 7,975 15,302 Total 6,960,027 3,498,052

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value	Below is a summary of assets measured at fair value as of March 31, 2017 and December 31, 2016. Fair Value Measurements Using March 31, 2017 Quoted Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 9,631,826 $ 9,631,826 $ — $ — Corporate debt securities 68,119,220 — 68,119,220 — Total $ 77,751,046 $ 9,631,826 $ 68,119,220 $ — Fair Value Measurements Using December 31, 2016 Quoted Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Money market funds $ 45,523,208 $ 45,523,208 $ — $ — Corporate debt securities 27,702,317 — 27,702,317 — Total $ 73,225,525 $ 45,523,208 $ 27,702,317 $ —

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2017
Investments Debt And Equity Securities [Abstract]
Summary of 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 following tables summarize the Company’s marketable securities: As of March 31, 2017 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 63,638,149 $ 2,411 $ (22,124 ) $ 63,618,436 Corporate debt securities 1 - 2 446,889 551 — 447,440 Total $ 64,085,038 $ 2,962 $ (22,124 ) $ 64,065,876 As of December 31, 2016 Maturity (in years) Amortized Cost Unrealized Gains Unrealized Losses Estimated Fair Value Corporate debt securities 1 or less $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715 Total $ 18,937,860 $ 901 $ (7,046 ) $ 18,931,715

Property and Equipment (Tables)

Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consist of the following: March 31, December 31, 2017 2016 Furniture and fixtures $ 333,670 $ 333,670 Computer equipment and office equipment 121,772 119,354 Leasehold improvements 152,217 152,217 607,659 605,241 Less accumulated depreciation and amortization (369,884 ) (343,795 ) Total $ 237,775 $ 261,446

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2017
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 months ended March 31, 2017: Total Options Weighted- Average Exercise Price Balance at December 31, 2016 3,393,813 $ 5.10 Granted 888,100 4.31 Exercised (51,174 ) 1.14 Cancelled (55,104 ) 4.42 Balance at March 31, 2017 4,175,635 $ 5.00
Summary of Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance at March 31, 2017: Warrants to purchase common stock 149,704 Common stock options issued and outstanding 4,175,635 Common stock authorized for future option grants 767,195 Common stock authorized for the ESPP 555,210 Shares issuable upon conversion of convertible note payable 2,626,713 Total 8,274,457

Organization and Basis of Pre21

Organization and Basis of Presentation - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation	Jul. 13, 2005
Accumulated deficit	$ 154,233,197	$ 150,632,452

Summary of Significant Accoun22

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2017USD ($)Segment	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)
Property, Plant and Equipment [Line Items]
Realized gains and losses on investments	$ 0	$ 0
Other-than-temporary declines in value of marketable securities	0
Impairment losses not recognized	$ 0
Unrecognized tax benefits that would, if recognized, affect the Company’s effective tax rate			$ 0
Number of operating segment | Segment	1
Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of the assets	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives of the assets	5 years

Summary of Significant Accoun23

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	6,960,027	3,498,052
ESPP shares pending issuance [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	7,975	15,302
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	149,704	149,704
Common stock options issued and outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	4,175,635	3,309,993
Shares issuable upon conversion of convertible note payable [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	2,626,713
Common stock subject to repurchase [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		23,053

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 77,751,046	$ 73,225,525
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	9,631,826	45,523,208
Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	68,119,220	27,702,317
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	9,631,826	45,523,208
Level 1 [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	9,631,826	45,523,208
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	68,119,220	27,702,317
Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 68,119,220	$ 27,702,317

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 64,085,038	$ 18,937,860
Unrealized Gains	2,962	901
Unrealized Losses	(22,124)	(7,046)
Estimated Fair Value	64,065,876	18,931,715
Corporate debt securities 1 or less years of maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	63,638,149	18,937,860
Unrealized Gains	2,411	901
Unrealized Losses	(22,124)	(7,046)
Estimated Fair Value	63,618,436	$ 18,931,715
Corporate debt securities 1 - 2 years of maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	446,889
Unrealized Gains	551
Estimated Fair Value	$ 447,440

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 607,659	$ 605,241
Less accumulated depreciation and amortization	(369,884)	(343,795)
Total	237,775	261,446
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	333,670	333,670
Computer equipment and office equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	121,772	119,354
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 152,217	$ 152,217

Note Payable - Additional Infor

Note Payable - Additional Information (Detail) - USD ($)	Feb. 15, 2017	Jan. 24, 2017	Mar. 31, 2017	Dec. 19, 2016	Jul. 31, 2010
Debt Instrument [Line Items]
Convertible note payable			$ 12,600,000
Novartis [Member] | Investment Agreement [Member]
Debt Instrument [Line Items]
Deferred revenue				$ 2,500,000
Novartis [Member] | Investment Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of outstanding shares will receive upon debt instrument conversion			19.00%
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	Novartis has the option to convert all or part of the Novartis Note into shares of the Company’s common stock upon a change in control of the Company or termination of the Collaboration Agreement by Novartis pursuant to certain provisions. If converted, the principal and accrued interest under the Novartis Note will convert 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. In the event the aggregate number of shares of common stock issued upon the conversion would exceed the lesser of 19.0% of the Company’s outstanding shares on a fully-diluted basis (i) at the inception of the Investment Agreement or (ii) on the conversion date, then only the lesser amount shall convert into shares of common stock and Novartis shall be repaid in cash for any remaining principal and unpaid interest after such conversion. Upon the occurrence of certain events of default, the Novartis Note requires the Company to repay the principal balance of the Novartis Note and any unpaid accrued interest.
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
Fair value of convertible note payable			$ 12,600,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2013	Jul. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants exercisable, outstanding	149,704
Stock-based compensation	$ 1,249,473	$ 901,924
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
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
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, outstanding				13,468
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, outstanding				136,236

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2017$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Total Options, Beginning balance | shares	3,393,813
Total Options, Granted | shares	888,100
Total Options, Exercised | shares	(51,174)
Total Options, Cancelled | shares	(55,104)
Total Options, Ending balance | shares	4,175,635
Weighted-Average Exercise Price, Beginning balance | $ / shares	$ 5.10
Weighted-Average Exercise Price, Granted | $ / shares	4.31
Weighted-Average Exercise Price, Exercised | $ / shares	1.14
Weighted-Average Exercise Price, Cancelled | $ / shares	4.42
Weighted-Average Exercise Price, Ending balance | $ / shares	$ 5

Stockholders' Equity - Summar30

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail)	Mar. 31, 2017shares
Equity [Abstract]
Warrants to purchase common stock	149,704
Common stock options issued and outstanding	4,175,635
Common stock authorized for future option grants	767,195
Common stock authorized for the ESPP	555,210
Shares issuable upon conversion of convertible note payable	2,626,713
Total	8,274,457

Collaboration and License Agr31

Collaboration and License Agreements - Additional Information (Detail)	Feb. 15, 2017USD ($)	Dec. 31, 2016USD ($)Deliverable	May 04, 2017USD ($)	Mar. 31, 2017USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Convertible note payable				$ 12,600,000
Collaboration Agreement [Member] | Novartis [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum milestone payments to be received upon achievement of certain milestones		$ 650,000,000
Percentage of development costs		50.00%
Required prior written notice period for termination of collaboration agreement		180 days
Percentage of reduction in milestone and royalty payments		50.00%
Number of significant deliverables | Deliverable		2
Collaboration revenue recognized over the period from upfront payment received		$ 50,000,000
Collaboration revenue recognized over the period from option exercise fee		7,000,000
Collaboration Agreement [Member] | Novartis [Member] | Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds due from option exercised			$ 7,000,000
Collaboration Agreement [Member] | Novartis [Member] | Upfront Payment [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable payment received		50,000,000
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
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
Deferred revenue		$ 2,500,000
Investment Agreement [Member] | Novartis [Member] | Convertible Promissory Note [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Principal amount of note issued	$ 15,000,000
Proceeds from issuance of convertible note payable	15,000,000
Convertible note payable	12,500,000
Reduction of outstanding receivable	$ 2,500,000
Investment Agreement [Member] | Novartis [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of outstanding shares will receive upon debt instrument conversion		19.00%

Commitments - Additional Inform

Commitments - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	May 31, 2015	Mar. 31, 2017	Mar. 31, 2016	Jul. 31, 2010
Operating Leased Assets [Line Items]
Rent expense		$ 94,501	$ 94,501
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
Future minimum payments for noncancelable operating lease		$ 1,500,000
Operating lease term September 2015 through September 2020 [Member]
Operating Leased Assets [Line Items]
Percentage of base rent escalator	3.00%
Rent expense	$ 32,784
Lease agreement rent expense for future period	$ 39,268