Cymabay Therapeutics (CBAY) 10-K 15 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	CBAY
Entity Registrant Name	CYMABAY THERAPEUTICS, INC.
Entity Central Index Key	1,042,074
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		58,501,794
Entity Public Float			$ 154,300,291

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 23,054	$ 10,495
Marketable securities	74,156	6,499
Receivable from collaboration	5,000
Prepaid expenses	1,208	1,369
Other current assets	126	165
Total current assets	103,544	18,528
Property and equipment, net	69	77
Other assets	634	754
Total assets	104,247	19,359
Current liabilities:
Accounts payable	1,311	899
Accrued liabilities	5,757	4,501
Warrant liability	6,091	1,145
Facility loan	3,108	2,700
Accrued interest payable	43	66
Total current liabilities	16,310	9,311
Facility loan, less current portion	2,990	6,098
Other liabilities		13
Total liabilities	19,300	15,422
Stockholders’ equity:
Preferred stock, $0.0001 par value: 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value: 100,000,000 shares authorized; 44,408,796 and 23,447,003 shares issued and outstanding as of December 31, 2017 and 2016, respectively	4	2
Additional paid-in capital	535,503	426,895
Accumulated other comprehensive loss	(44)	(1)
Accumulated deficit	(450,516)	(422,959)
Total stockholders’ equity	84,947	3,937
Total liabilities and stockholders’ equity	$ 104,247	$ 19,359

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 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	100,000,000	100,000,000
Common stock, shares issued	44,408,796	23,447,003
Common stock, shares outstanding	44,408,796	23,447,003

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Collaboration revenue	$ 10,000
Operating expenses:
Research and development	18,938	$ 15,941
General and administrative	12,387	9,645
Total operating expenses	31,325	25,586
Loss from operations	(21,325)	(25,586)
Other income (expense):
Interest income	621	176
Interest expense	(1,080)	(1,337)
Other (expense) income, net	(5,773)	76
Net loss	(27,557)	(26,671)
Net loss	(27,557)	(26,671)
Other comprehensive income (loss):
Unrealized (loss) gain on marketable securities	(43)	20
Other comprehensive (loss) income	(43)	20
Comprehensive loss	$ (27,600)	$ (26,651)
Basic net loss per common share	$ (0.79)	$ (1.14)
Diluted net loss per common share	$ (0.79)	$ (1.14)
Weighted average common shares outstanding used to calculate basic net loss per common share	34,903,960	23,447,003
Weighted average common shares outstanding used to calculate diluted net loss per common share	34,903,960	23,447,003

Statement of Shareholders' Equi

Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at beginning of period at Dec. 31, 2015	$ 28,115	$ 2	$ 424,422	$ (21)	$ (396,288)
Balance at beginning of period (in shares) at Dec. 31, 2015		23,447,003
Stock-based compensation expense	2,473		2,473
Net loss	(26,671)				(26,671)
Net unrealized gain (loss) on marketable securities	20			20
Balance at end of period at Dec. 31, 2016	3,937	$ 2	426,895	(1)	(422,959)
Balance at end of period (in shares) at Dec. 31, 2016		23,447,003
Issuance of common stock upon exercise of warrants, value	1,058		1,058
Issuance of common stock upon exercise of warrants (Shares)		99,207
Issuance of common stock upon exercise of stock options and incentive awards	2,196		2,196
Issuance of common stock upon exercise of stock options and incentive awards (Shares)		607,138
Stock-based compensation expense	4,920		4,920
Issuance of common stock, value	100,436	$ 2	100,434
Issuance of common stock, (in shares)		20,255,448
Net loss	(27,557)				(27,557)
Net unrealized gain (loss) on marketable securities	(43)			(43)
Balance at end of period at Dec. 31, 2017	$ 84,947	$ 4	$ 535,503	$ (44)	$ (450,516)
Balance at end of period (in shares) at Dec. 31, 2017		44,408,796

Statement of Shareholders' Equ6

Statement of Shareholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Statement Of Stockholders Equity [Abstract]
Stock issuance cost	$ 7,047

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (27,557)	$ (26,671)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	35	29
Stock-based compensation expense	4,920	2,473
Net accretion and amortization of investments in marketable securities	(199)	125
Non-cash interest associated with debt discount accretion	437	476
Change in fair value of warrant liability	5,773	(75)
Changes in assets and liabilities:
Accounts receivable	(5,000)
Other current assets	(98)	165
Prepaid expenses	161	(761)
Other assets	120	(13)
Accounts payable	412	(109)
Accrued liabilities	1,387	1,015
Accrued interest payable	(23)	(7)
Net cash used in operating activities	(19,632)	(23,353)
Investing activities
Purchases of property and equipment	(27)	(42)
Purchases of marketable securities	(98,385)	(22,906)
Proceeds from maturities of marketable securities	30,884	50,076
Net cash (used in) provided by investing activities	(67,528)	27,128
Financing activities
Proceeds from issuance of common stock, net of issuance costs	100,436
Proceeds from issuance of common stock pursuant to equity award plans	2,189
Proceeds from issuance of common stock upon exercise of warrants	231
Repayment of facility loan principal	(3,137)	(986)
Net cash provided by (used in) financing activities	99,719	(986)
Net increase in cash and cash equivalents	12,559	2,789
Cash and cash equivalents at beginning of period	10,495	7,706
Cash and cash equivalents at end of period	23,054	10,495
Supplemental disclosure
Cash paid for interest	666	866
Supplemental non-cash investing and financing activities
Issuance of common stock upon warrant exercises	827
Net change in accrued financing costs	$ (144)	$ 144

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business CymaBay Therapeutics, Inc. (the “Company” or “CymaBay”) is a clinical-stage biopharmaceutical company focused on developing and providing access to innovative therapies for patients with liver and other chronic diseases with high unmet medical need. The Company’s two key clinical development candidates are seladelpar (MBX-8025) and arhalofenate. Seladelpar is currently being developed for the treatment of primary biliary cholangitis (PBC) and the Company is also planning to develop seladelpar for the treatment of nonalcoholic steatohepatitis (NASH). Arhalofenate is being developed for the treatment of gout and has been out-licensed in the United States. The Company was incorporated in Delaware in October 1988 as Transtech Corporation. The Company’s headquarters and operations are located in Newark, California and it operates in one segment. The Company is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has irrevocably elected not to avail itself of this exemption from new or revised accounting standards, and, therefore, is subject to the same new or revised accounting standards as other public companies that are not emerging growth companies. Liquidity The Company has incurred net operating losses and negative cash flows from operations since its inception. During the year ended December 31, 2017, the Company incurred a net loss of $27.6 million and used $19.6 million of cash in operations. At December 31, 2017, the Company had an accumulated deficit of $450.5 million. CymaBay expects to incur substantial research and development expenses as it continues to study its product candidates in clinical trials. To date, none of the Company’s product candidates have been approved for marketing and sale, and the Company has not recorded any revenue from product sales. As a result, management expects operating losses to continue in future years. The Company’s ability to achieve profitability is dependent primarily on its ability to successfully develop, acquire or in-license additional product candidates, continue clinical trials for product candidates currently in clinical development, obtain regulatory approvals, and support commercialization activities for partnered product candidates. Products developed by the Company will require approval of the U.S. Food and Drug Administration (FDA) or a foreign regulatory authority prior to commercial sale. The regulatory approval process is expensive, time-consuming, and uncertain, and any denial or delay of approval could have a material adverse effect on the Company. Even if approved, the Company’s products may not achieve market acceptance and will face competition from both generic and branded pharmaceutical products. As of December 31, 2017, the Company’s cash, cash equivalents and marketable securities totaled $97.2 million. The Company believes these funds, together with net proceeds of $135.5 million received in the public offering in February 2018, and a $5 million milestone payment received pursuant to the Company’s license agreement with Kowa in January 2018, are sufficient to fund the Company’s current operating plan into 2021.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Use of Estimates The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP), which requires management to make informed estimates and assumptions that impact the amounts and disclosures reported in the financial statements and accompanying notes. Accounting estimates and assumptions are inherently uncertain. Management bases its estimates on historical experience and on assumptions believed to be reasonable under the circumstances. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Actual results could differ materially from those estimates and assumptions. The Company believes significant judgment is involved in determining and in estimating the valuation of stock-based compensation, accrued clinical expenses, and equity instrument valuations. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. Estimates are assessed each reporting period and updated to reflect current information and any changes in estimates will generally be reflected in the period first identified. Fair Value of Financial Instruments The Company’s financial instruments during the periods reported consist of cash and cash equivalents, marketable securities, accounts receivable, prepaid expenses, other current assets, accounts payable, accrued interest payable, accrued expenses, the facility loan, and warrant liabilities. Fair value estimates of these instruments are made at a specific point in time, based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment. The carrying amounts of financial instruments such as cash and cash equivalents, accounts receivable, prepaid expenses, other current assets, accounts payable, accrued expenses, and accrued interest payable approximate the related fair values due to the short maturities of these instruments. Based on prevailing borrowing rates available to the Company for loans with similar terms, the Company believes the fair value of the facility loan, considering level 2 inputs, approximates its carrying value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Assets and liabilities that are measured at fair value are reported using a three-level fair value hierarchy that prioritizes the inputs used to measure fair value. This hierarchy maximizes the use of observable inputs and maximizes the use of unobservable inputs and is as follows: Level 1—Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs other than quoted prices in active markets that are observable for the asset or liability, either directly or indirectly. Level 3—Inputs that are significant to the fair value measurement and are unobservable (i.e. supported by little market activity), which requires the reporting entity to develop its own valuation techniques and assumptions. The following tables present the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis using the above input categories (in thousands): As of December 31, 2017 (In thousands) Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 12,822 $ — $ — $ 12,822 Commercial paper — 6,035 — 6,035 Total cash equivalents 12,822 6,035 — 18,857 Short-term investments: Commercial paper — 35,886 — 35,886 Corporate debt securities — 19,760 — 19,760 Asset-backed securities — 11,060 — 11,060 U.S. treasury securities — 7,450 7,450 Total short-term investments — 74,156 — 74,156 Total assets measured at fair value $ 12,822 $ 80,191 $ — $ 93,013 Warrant liability $ — $ — $ 6,091 $ 6,091 Total liabilities measured at fair value $ — $ — $ 6,091 $ 6,091 As of December 31, 2016 (In thousands) Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 9,456 $ — $ — $ 9,456 Commercial paper — 599 — 599 Corporate debt securities — 500 — 500 Total cash equivalents 9,456 1,099 — 10,555 Short-term investments: Commercial paper — 4,295 — 4,295 Corporate debt securities — 2,204 — 2,204 Total short-term investments — 6,499 — 6,499 Total assets measured at fair value $ 9,456 $ 7,598 $ — $ 17,054 Warrant liability $ — $ — $ 1,145 $ 1,145 Total liabilities measured at fair value $ — $ — $ 1,145 $ 1,145 The Company estimates the fair value of its corporate debt, asset backed securities, and U.S. treasury securities by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads; benchmark securities; prepayment/default projections based on historical data; and other observable inputs. There were no transfers between Level 1 and Level 2 during the periods presented. As of December 31, 2017 and 2016, financial instruments measured using Level 3 inputs consisted of the Company’s warrants, which are accounted for as liabilities. During the year, the Company changed its valuation technique and began to value its warrant liability using a Black-Scholes option pricing model, the inputs for which include: exercise price of the warrants, market price of the underlying common shares, dividend yield, expected term, expected volatility, and a risk-free interest rate. Changes to any of these inputs can have a significant impact on the estimated fair value of the warrants. Historically, the Company used a binomial option pricing model to value its warrant liabilities. The inputs for the binomial model are similar to the Black-Scholes model but also incorporate other more complex inputs that, in the Company’s case, have previously included the expected timing, probability and valuation impact of certain potential strategic events. Management concluded that no potential strategic events were expected to occur that, upon their announcement, could significantly impact the warrant liabilities valuation prior to their expiration beginning in late 2018 and ending in early 2019. The following tables set forth a summary of the changes in the fair value of our liabilities measured using Level 3 inputs (in thousands): For the Twelve Months Ended December 31, 2017 2016 Balance, beginning of period $ 1,145 $ 1,220 Issuance of financial instrument — — Change in fair value 5,773 (75 ) Settlement of financial instrument (827 ) — Balance, end of period $ 6,091 $ 1,145 Cash, Cash Equivalents, and Marketable Securities The Company considers all highly liquid investments with a remaining maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking, interest-bearing, demand money market accounts, corporate debt securities, and commercial paper. The Company invests excess cash in marketable securities with high credit ratings that are classified in Level 1 and Level 2 of the fair value hierarchy. These securities consist primarily of corporate debt, commercial paper, asset-backed securities, and U.S. treasury securities and are classified as “available-for-sale.” The Company considers marketable securities as short-term investments if the maturity date is less than one year from the balance sheet date. The Company considers marketable securities as long-term investments if the maturity date is in excess of one year of the balance sheet date. Realized gains and losses from the sale of marketable securities, if any, are calculated using the specific-identification method. Realized gains and losses and declines in value judged to be other-than- temporary are included in interest income or expense in the statements of operations and comprehensive loss. Unrealized holding gains and losses are reported in accumulated other comprehensive loss in the balance sheets. To date, the Company has not recorded any impairment charges on its marketable securities related to other-than-temporary declines in market value. In determining whether a decline in market value is other-than-temporary, various factors are considered, including the cause, duration of time and severity of the impairment, any adverse changes in the investees’ financial condition, and the Company’s intent and ability to hold the security for a period of time sufficient to allow for an anticipated recovery in market value. Concentration of Credit Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to a concentration of credit risk to the extent of the fair value recorded in the balance sheet. The Company invests cash that is not required for immediate operating needs primarily in highly liquid instruments that bear minimal risk. The Company has established guidelines relating to the quality, diversification, and maturities of securities to enable the Company to manage its credit risk. We are exposed to credit risk in the event of a default by the financial institutions holding our cash, cash equivalents and investments and issuers of investments to the extent recorded on the balance sheets. Certain materials and key components that the Company utilizes in its operations are obtained through single suppliers. Since the suppliers of key components and materials must be named in a new drug application (NDA) filed with the U.S. Food and Drug Administration (FDA) for a product, significant delays can occur if the qualification of a new supplier is required. If delivery of material from the Company’s suppliers were interrupted for any reason, the Company may be unable to supply any of its product candidates for clinical trials. Property and Equipment Property and equipment is recorded at cost, less accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method, and the cost is amortized over the estimated useful lives of the respective assets, generally three to seven years. Leasehold improvements are amortized over the shorter of the useful lives or the non-cancelable term of the related lease. Maintenance and repair costs are charged as expense in the statements of operations and comprehensive loss as incurred. Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss is recognized if the estimated undiscounted future cash flow expected to result from the use and eventual disposition of an asset is less than the carrying amount. While the Company’s current and historical operating losses and cash flows are indicators of impairment, the Company believes the future cash flows to be received support the carrying value of its long-lived assets. Accordingly, the Company has not recognized any impairment losses as of December 31, 2017. Deferred Rent The Company records its costs under facility operating lease agreements as rent expense. Rent expense is recognized on a straight-line basis over the non-cancelable term of the operating lease. The difference between the actual amounts paid and amounts recorded as rent expense is recorded as deferred rent in the accompanying balance sheets. Revenue Recognition The Company recognizes revenue when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred or services have been rendered, (iii) the price is fixed or determinable, and (iv) collectability is reasonably assured. Payments received in advance of work performed are recorded as deferred revenue and recognized when earned. Collaboration and license agreements may include non-refundable upfront license fees, contingent consideration payments based on the achievement of defined collaboration objectives and royalties on sales of commercialized products. The Company’s performance obligations under collaboration and license agreements may include the license or transfer of intellectual property rights, obligations to provide research and development services and related materials and obligations to participate on certain development and/or commercialization committees with the collaborators. If the Company determines that multiple deliverables in an arrangement exist, the consideration is allocated to one or more units of accounting based upon the relative-selling-price of each element in an arrangement. The relative-selling-price used for each deliverable is based on vendor-specific objective evidence, if available, third-party evidence if vendor-specific objective evidence is not available, or estimated selling price if neither vendor-specific or third-party evidence is available. The Company identifies deliverables at the inception of the arrangement. Each deliverable is accounted for as a separate unit of accounting if both of the following criteria are met: (1) the delivered item or items have value to the customer on a standalone basis and (2) for an arrangement that includes a general right of return relative to the delivered items, delivery or performance of the undelivered items is considered probable and substantially in the Company’s control. Non-refundable upfront payments received and allocated to separate units of accounting are recognized as revenue when the four basic revenue recognition criteria are met for each unit of accounting. The Company recognizes payments that are contingent upon achievement of a substantive milestone in their entirety in the period in which the milestone is achieved. Milestones are defined as events that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones subject to this guidance. Further, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables and payment terms within the agreement and commensurate with the Company’s performance to achieve the milestone after commencement of the agreement. Any contingent payment that becomes payable upon achievement of events that are not considered substantive milestones are allocated to the units of accounting previously identified at the inception of an arrangement when the contingent payment is received and revenue is recognized based on the revenue recognition criteria for each unit of accounting. Research and Development Expenses Research and development expenses consist of costs incurred in identifying, developing, and testing product candidates. These expenses consist primarily of costs for research and development personnel, including related stock-based compensation; contract research organizations (CRO) and other third parties that assist in managing, monitoring, and analyzing clinical trials; investigator and site fees; laboratory services; consultants; contract manufacturing services; non-clinical studies, including materials; and allocated expenses, such as depreciation of assets, and facilities and information technology that support research and development activities. Research and development costs are expensed as incurred, including expenses that may or may not be reimbursed under research and development funding arrangements. Payments made prior to the receipt of goods or services to be used in research and development are recorded as prepaid assets until the goods are received or services are rendered. Such payments are evaluated for current or long term classification based on when they will be realized. The Company records expenses related to clinical studies and manufacturing development activities based on its estimates of the services received and efforts expended pursuant to contracts with multiple CROs and manufacturing vendors that conduct and manage these activities on its behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract, and may result in uneven payment flows. There may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense. Payments under some of these contracts depend on factors such as the successful enrollment of subjects and the completion of clinical trial milestones. In amortizing or accruing service fees, the Company estimates the time period over which services will be performed, enrollment of subjects, number of sites activated and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the Company will adjust the accrued or prepaid expense balance accordingly. To date, there have been no material differences from the Company’s estimates to the amounts actually incurred. Stock-Based Compensation Employee and director stock-based compensation is measured at fair value on the grant date of the award. Compensation cost is recognized as expense on a straight-line basis over the vesting period for options and on an accelerated basis for stock options with performance conditions, net of estimated forfeitures. For stock options with performance conditions, the Company evaluates the probability of achieving performance conditions at each reporting date. The Company begins to recognize the expense when it is deemed probable that the performance conditions will be met. The Company uses the Black-Scholes option pricing model to determine the fair value of stock option awards. The determination of fair value for stock-based awards using an option-pricing model requires management to make certain assumptions regarding subjective input variables such as expected term, dividends, volatility and risk-free rate. The Company is also required to make estimates as to the probability of achieving the specific performance criteria. If actual results are not consistent with the Company’s assumptions and judgments used in making these estimates, the Company may be required to increase or decrease compensation expense, which could be material to the Company’s results of operations. Equity awards granted to non-employees are valued using the Black-Scholes option pricing model. Stock-based compensation expense for nonemployee services is subject to remeasurement as the underlying equity instruments vest and is recognized as an expense over the period during which services are received. Common Stock Warrant Liabilities The Company’s outstanding common stock warrants issued in connection with certain equity and debt financings that occurred in 2013 through 2015 are classified as liabilities in the accompanying balance sheets because of certain contractual terms that preclude equity classification. The Company estimates the fair value of common stock warrants at each reporting period until the earlier of the exercise of the warrants, at which time the liability will be revalued and reclassified to stockholders’ equity, or expiration of the warrants. The determination of fair value of these common stock warrants requires management to make certain assumptions regarding subjective input variables such as timing, probability and valuation impact of certain potential strategic events, expected term, dividends, expected volatility and risk-free interest rates. If actual results are not consistent with the Company’s assumptions and judgments used in making these estimates, the Company may be required to increase or decrease other (expense) income, net, which could be material to the Company’s results of operations. Income Taxes The Company utilizes the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on differences between the financial reporting and the tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. A valuation allowance is recorded when it is more likely than not that all or part of a deferred tax asset will not be realized. When the Company establishes or reduces the valuation allowance related to the deferred tax assets, the provision for income taxes will increase or decrease, respectively, in the period such determination is made. The accounting guidance for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial 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 based on the technical merits of the position. The Company is required to file federal and state income tax returns in the United States. The preparation of these income tax returns requires the Company to interpret the applicable tax laws and regulations in effect that could affect the amount of tax paid to these jurisdictions. In December 2017, Securities and Exchange Commission (“SEC”) staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act The Company records interest related to income tax reserves, if any, as interest expense, and any penalties would be recorded as other expense in the statements of operations and comprehensive loss. There was no interest or penalties related to income tax reserves during the years ended December 31, 2017 and 2016. Comprehensive Loss Comprehensive loss includes net loss and net unrealized gains and losses on marketable securities, which are presented in a single continuous statement. Comprehensive loss is disclosed in the statements of stockholders’ equity, and is stated net of related tax effects, if any. Net Income (Loss) Per Common Share Basic net loss per share of common stock is based on the weighted average number of shares of common stock outstanding equivalents during the period. Diluted net loss per share of common stock is calculated as the weighted average number of shares of common stock outstanding adjusted to include the assumed exercises of stock options and common stock warrants, if dilutive. The calculation of diluted loss per share also requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the common stock warrants and the presumed exercise of such securities are dilutive to earnings (loss) per share for the period, adjustments to net income or net loss used in the calculation are required to remove the change in fair value of the common stock warrant liability for the period. Likewise, adjustments to the denominator are required to reflect the related dilutive shares. In all periods presented, the Company’s outstanding stock options were excluded from the calculation of net loss per share because the effect would be antidilutive. The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share amounts): Year Ended December 31, 2017 2016 Numerator: Net loss allocated to common stock—basic $ (27,557 ) $ (26,671 ) Adjustment for revaluation of warrants — — Net loss allocated to common stock—diluted $ (27,557 ) $ (26,671 ) Denominator: Weighted average number of common stock shares outstanding - basic 34,903,960 23,447,003 Dilutive common stock warrants — — Weighted average number of common stock shares outstanding - diluted 34,903,960 23,447,003 Net loss per share—basic $ (0.79 ) $ (1.14 ) Net loss per share—diluted $ (0.79 ) $ (1.14 ) The following table shows the total outstanding securities considered anti-dilutive and therefore excluded from the computation of diluted net loss per share (in thousands): Year Ended December 31, 2017 2016 Common stock warrants 1,461 1,667 Common stock options 4,055 2,394 Performance-based stock options 301 327 Incentive awards 130 239 5,947 4,627 Recent Accounting Pronouncements Accounting Standards Update 2014-09 In May 2014, the FASB issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers and related amendments. Subsequently, the Financial Accounting Standards Board (“the FASB”) issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; and ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients. This guidance outlines a new, and single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes nearly all of the existing revenue recognition guidance, including industry-specific guidance. This new revenue recognition model provides a five-step analysis in determining when and how revenue is recognized. The new model will require revenue recognition to depict the transfer of promised goods or services to customers in an amount that reflects the consideration a company expects to receive in exchange for those goods or services. The new revenue standard permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). The Company plans to adopt the new revenue standard in the first quarter of 2018 using the modified retrospective method. To date, the Company’s revenues have been derived from license and collaboration agreements. The consideration that the Company is eligible to receive under such agreements includes upfront payments, milestone payments, and royalties. The Company has assessed its contracts with customers under the five-step process and analyzed such contracts to determine the differences in the accounting treatment under the new revenue standard compared to that of the current accounting standard. The new revenue standard differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments and royalties. The Company has substantially completed its assessment of the new revenue standard for the accounting of its license and collaboration agreements and related financial statement disclosures. The impact of adopting the new revenue standard will not be material and the Company does not expect to record any cumulative-effect adjustment to accumulated deficit upon adoption. The new standard will require more robust disclosures than required by previous guidance, including disclosures related to disaggregation of revenue, discussion of performance obligations, estimates of variable consideration, the judgments made in revenue recognition determinations, adjustments to revenue which relate to activities from previous periods, any significant reversals of revenue, and costs to obtain or fulfill contracts. Accounting Standards Update 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The new standard requires the recognition of assets and liabilities arising from lease transactions on the balance sheet and the disclosure of key information about leasing arrangements. Accordingly, a lessee will recognize a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. Both the asset and liability will initially be measured at the present value of the future minimum lease payments over the lease term. Subsequent measurement, including the presentation of expenses and cash flows, will depend on the classification of the lease as either a finance or an operating lease. Initial costs directly attributable to negotiating and arranging the lease will be included in the asset. Lessees will also be required to provide additional qualitative and quantitative disclosures regarding the amount, timing and uncertainty of cash flows arising from leases. The new standard is effective for fiscal years beginning after December 15, 2018, and interim periods therein. Early adoption is permitted. The Company is currently evaluating the impact this guidance will have on its financial statements. Accounting Standards Update 2016-09 In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting Accounting Standards Update 2017-09 In May 2017, FASB issued ASU No. 2017-09, Compensation-Stock Compensation (Topic 718) - Scope of Modification Accounting Accounting Standards Update 2017-11 In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share Distinguishing Liabilities from Equity Derivatives and Hedging

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Marketable Securities	3. Marketable Securities Marketable available-for-sale securities as of December 31, 2017 and 2016 consist of the following (in thousands): Gross Gross Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value As of December 31, 2017: Commercial paper 35,886 — — 35,886 Corporate debt securities 19,785 — (25 ) 19,760 Asset-backed securities 11,070 — (10 ) 11,060 U.S. treasury securities 7,459 — (9 ) 7,450 $ 74,200 $ — $ (44 ) $ 74,156 Gross Gross Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value As of December 31, 2016: Commercial paper 4,295 — — 4,295 Corporate debt securities 2,205 — (1 ) 2,204 $ 6,500 $ — $ (1 ) $ 6,499 As of December 31, 2017 and 2016, the remaining contractual maturities of the Company’s commercial paper, corporate debt securities, asset-backed securities, and U.S. treasury securities were less than 1

Certain Balance Sheet Items

Certain Balance Sheet Items	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Certain Balance Sheet Items	4. Certain Balance Sheet Items Property and equipment consist of the following (in thousands): December 31, December 31, 2017 2016 Office and computer equipment $ 177 $ 177 Purchased software 83 83 Furniture and fixtures 65 38 Leasehold improvements 65 65 Total 390 363 Less accumulated depreciation and amortization (321 ) (286 ) Property and equipment, net $ 69 $ 77 Accrued liabilities consist of the following (in thousands): December 31, December 31, 2017 2016 Accrued compensation $ 2,416 $ 1,839 Accrued pre-clinical and clinical trial expenses 2,929 1,623 Accrued professional fees 288 982 Other accruals 124 57 Total accrued liabilities $ 5,757 $ 4,501

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration and License Agreements	5. Collaboration and License Agreements Kowa Pharmaceuticals America, Inc. On December 30, 2016, the Company entered into a license agreement with Kowa Pharmaceuticals America, Inc. (“Kowa”). Pursuant to the license agreement, the Company granted to Kowa an exclusive license, and right to sublicense, certain patent rights and technology related to arhalofenate. Kowa will have exclusive rights to, among other things, develop, use, manufacture, sell and otherwise exploit the licensed technology in the United States (including all possessions and territories). At Kowa’s option, the Company may also facilitate the placement of arhalofenate product manufacturing orders under the terms of the Company’s existing contract manufacturing agreements. In addition, the Company will complete specified in-process stability testing and non-clinical development services and will participate on a Joint Advisory Committee (“JAC”). Finally, the Company will transfer to Kowa certain arhalofenate product on hand. Under the license agreement, Kowa agreed to pay the Company a non-refundable up-front payment of $5 million upon contract execution. Additionally, Kowa agreed to pay the Company $5 million upon initiation of a study evaluating the pharmacokinetics of arhalofenate in subjects with renal impairment, an additional milestone payment of $5 million on initiation of a Phase 3 study, and up to $190 million in payments based upon the achievement of other specific development and sales milestones. Finally, the Company will receive tiered, double digit royalties on any product sales and a percentage of any revenue earned by Kowa from sublicensing. The Company identified the following three performance deliverables under the license agreement: 1) transfer of intellectual property rights, inclusive of the related technology know-how conveyance and contract manufacturing rights and privileges (“license and know-how”), 2) the obligation to perform specific ongoing research and non-clinical development services, and 3) the delivery of arhalofenate product on hand. The Company’s participation on the JAC was not determined to be a deliverable because of the Company’s ability to elect to terminate its participation. The Company concluded that the license, the know-how and contract manufacturing rights and privileges together represent a single deliverable, and therefore together should be accounted for as a single unit of accounting. The research and development services and delivery of arhalofenate product each also represent separate deliverables, and therefore each should be accounted for as separate units of accounting. There was no separate consideration identified in the agreement for the deliverables and there was no right of return under the agreement. The Company considered the provisions of the multiple-element arrangement guidance in determining whether the deliverables outlined above have standalone value. The transfer of license and know-how has standalone value separate from the research and development services and delivery of arhalofenate product, as the agreement allows Kowa to sublicense its rights to the acquired license to a third party. Further, the Company believes that Kowa has research and development expertise with compounds similar to those licensed under the agreement, and the Company has also granted Kowa the rights to either order arhalofenate product from the Company’s existing contract manufacturers, or to enter into arrangements with other third parties to develop and manufacture arhalofenate product, thereby allowing Kowa to realize the value of the license and know-how. The license and know-how revenue will be recognized upon the substantial completion of the transfer of know-how. The research and development services will be recognized as revenue over the estimated period services are delivered. The arhalofenate product will be recognized as revenue upon delivery. The Company also determined the relative selling prices of the identified units of account in accordance with the multi-element arrangement guidance. The Company considered but did not use Vendor Specific Objective Evidence (VSOE) of fair value or third-party evidence (TPE) but instead selected management’s best estimate of selling price (BESP) due to the uniqueness of the Kowa license arrangement and its lack of comparability to other licensing arrangements in the biopharmaceutical industry. In the first quarter of 2017, the $5 million upfront consideration due upon contract initiation was paid and the Company allocated this consideration to the three identified units of account using the relative selling price method, with revenue to be recognized based on the satisfaction of all revenue recognition criteria for each unit of accounting. As the Company completed all activities necessary to transfer the license and knowhow deliverable to Kowa and had satisfied all other revenue recognition criteria, $4.8 million of the upfront consideration allocated to this deliverable was recognized as collaboration revenue in the first quarter of 2017. The Company also recognized immaterial revenue associated with the provision of the research and non-clinical development services deliverable. The remaining $0.2 million of upfront consideration was allocated to the arhalofenate product deliverable and was recognized as collaboration revenue upon delivery of the drug product to Kowa and satisfaction of other revenue recognition criteria in the fourth quarter of 2017. The Company determined the future contingent payments related to the development activities do not meet the definition of a milestone because the achievement of these events solely depends on Kowa’s performance. Under current revenue recognition rules, these amounts must be allocated to the Kowa arrangements’ three identified units of account when they become billable under the contract and recognized as revenue based on the satisfaction of the revenue recognition criteria for those respective units of accounting. The Company also determined that the future contingent payments related to the U.S. sales milestones are recognizable as revenue upon achievement of those specific sales milestones. In the fourth quarter of 2017, Kowa became obligated under the agreement to pay the first $5 million contingent payment to the Company upon Kowa’s initiation of a study evaluating the pharmacokinetics of arhalofenate in subjects with renal impairment. As of December 31, 2017, no amounts have been recognized as collaboration revenue for the remaining contingent payments as no amounts had been earned. Janssen Pharmaceutical NV and Janssen Pharmaceuticals, Inc. In June 2006, the Company entered into an exclusive worldwide, royalty-bearing license to seladelpar and certain other PPARδ compounds (the “PPARδ Products”) with Janssen Pharmaceutical NV (Janssen NV), with the right to grant sublicenses to third parties to make, use and sell such PPARδ Products. Under the terms of the agreement, the Company has full control and responsibility over the research, development and registration of any PPARδ Products and is required to use diligent efforts to conduct all such activities. Janssen NV has the sole responsibility for the preparation, filing, prosecution, maintenance of, and defense of the patents with respect to, the PPARδ Products. Janssen NV has a right of first negotiation under the agreement to license a particular PPARδ Product from the Company in the event that the Company elects to seek a third party corporate partner for the research, development, promotion, and/or commercialization of such PPARδ Products. Under the terms of the agreement Janssen NV is entitled to receive up to an 8% royalty on net sales of PPARδ Products. In June 2010, the Company entered into two development and license agreements with Janssen Pharmaceuticals, Inc. (Janssen), a subsidiary of Johnson and Johnson, to further develop and discover undisclosed metabolic disease target agonists for the treatment of Type 2 diabetes and other disorders and received a one-time nonrefundable technology access fee related to the agreements. The Company received a termination notice from Janssen, effectively ending these development and licensing agreements in early April 2015. In December 2015, the Company exercised an option pursuant to the terms of one of the original agreements to continue work to research, develop and commercialize compounds with activity against an undisclosed metabolic disease target. Janssen granted the Company an exclusive, worldwide license (with rights to sublicense) under the Janssen know-how and patents to research, develop, make, have made, use, offer for sale and sell such compounds. The Company has full control and responsibility over the research, development and registration of any products developed and/or discovered from the metabolic disease target and is required to use diligent efforts to conduct all such activities. No amounts were incurred or accrued for this agreement as of and for the years ended December 31, 2017 and 2016. DiaTex, Inc. In June 1998, the Company entered into a license agreement with DiaTex, Inc. (DiaTex) relating to products containing halofenate, its enantiomers, derivatives, and analogs (the licensed products). The license agreement provides that DiaTex and the Company are joint owners of all of the patents and patent applications covering the licensed products and methods of producing or using such compounds, as well as certain other know-how (the covered IP). As part of the license agreement, the Company received an exclusive worldwide license, including as to DiaTex, to use the covered IP to develop and commercialize the licensed products. The Company also retained the right to sub-license the covered IP. The license agreement contains a $2,000 per month license fee as well as a requirement to make additional payments for development achievements and royalty payments on any sales of licensed products. DiaTex is entitled to up to $0.8 million for the future development of arhalofenate, as well as royalty payments on commercial sales of products containing arhalofenate. No development payments were made or due as of and for the years ended December 31, 2017 and 2016 and no royalties have been paid to date. In December 2016, the agreement was amended by the parties to change the timing of a specified development milestone.

Facility Loans

Facility Loans	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Facility Loans	6. Facility Loans 2013 Term Loan Facility On September 30, 2013, the Company entered into a facility loan agreement with Silicon Valley Bank and Oxford Finance LLC (referred to herein as the lenders) for a total loan amount of $10.0 million of which the first tranche of $5.0 million was drawn as part of the Company’s September 2013 financing, referred to here as the 2013 Term Loan Facility. The loan had a fixed interest rate of 8.75% payable as interest only for twelve months and a thirty-six month loan amortization period thereafter, with a final interest payment of $0.3 million at the end of the loan period. The second tranche of $5.0 million became available to the Company upon its February 24, 2015 announcement of the achievement of positive Phase 2b data for the Company’s product candidate arhalofenate and remained available to the Company until June 30, 2015. On June 30, 2015, the second tranche portion of the loan facility expired unused by the Company. At the time the first $5 million tranche of the facility loan was drawn down, the Company issued warrants exercisable for a total of 121,739 shares of the Company’s common stock to the lenders at an exercise price of $5.00 per share. Upon issuance, the fair value of a warrant liability was recorded and is being revalued at each balance sheet date until the warrants are exercised or expire. 2015 Term Loan Facility On August 7, 2015, the Company entered into a Loan and Security Agreement pursuant to which it refinanced its existing 2013 Term Loan Facility with Oxford Finance LLC and Silicon Valley Bank, for an aggregate amount of up to $15 million, referred to here as the 2015 Term Loan Facility. The first $10 million tranche of this new loan facility was made available to the Company immediately upon the closing and was used in part to retire all $4.1 million of the Company’s existing debt outstanding under the 2013 Term Loan Facility, and to settle accrued interest and closing costs with the lenders. The remaining $5 million, referred to as the second tranche, was made available to the Company until March 31, 2016, for draw down upon the achievement of a specified milestone. Because the present value of the future cash flows under the modified loan terms did not exceed the present value of the future cash flows under the previous loan terms by more than 10%, the Company treated this refinancing as a modification. The remaining debt discount costs will be amortized over the remaining term of the Loan and Security Agreement using the effective interest rate method. The $5.0 million second tranche expired unused in March 2016 as the second draw milestone was not achieved. The loan bears interest at 8.77%. The Company is required to make 12 monthly interest only payments after the funding date followed by a repayment schedule equal to 36 equal monthly payments of interest and principal. Upon maturity, the remaining balance of the first tranche and a final payment equal to 6.50% of the original principal amount advanced of the applicable tranche are payable. At the closing, the Company also agreed to pay a facility fee of 1.00% of the 2015 Term Loan Facility commitment. In addition, the Company issued warrants exercisable for a total of 114,436 shares of its common stock to the lenders at an exercise price of $2.84 per share, and with a term of ten years. Upon issuance, the fair value of a warrant liability of $0.3 million was recorded in the accompanying balance sheet and is being revalued at each balance sheet date until the warrants are exercised or expire. The Company’s obligations under the term loan facility are secured, subject to customary permitted liens and other agreed upon exceptions, by a perfected first priority interest in all of the Company’s tangible and intangible assets, excluding intellectual property. The Company also entered into a negative pledge agreement with the lenders pursuant to which the Company has agreed not to encumber any intellectual property. The 2015 Term Loan Facility contains customary representations and warranties and customary affirmative and negative covenants applicable to the Company, and also includes defined customary events of default that include but are not limited to a material adverse change in the Company’s business, operations or condition (financial or otherwise), a material impairment of the prospect of repayment of any portion of the term loan, or a material impairment in the perfection or priority of the collateral agent’s lien in the collateral or in the value of such collateral. As of December 31, 2017, the Company was in compliance with the term loan covenants and there were no events of default. The term loan facility, debt discounts and final payment balances as of December 31, 2017 and 2016 are as follows (in thousands): December 31, 2017 2016 Principal payments due under the loan facility $ 5,877 $ 9,014 Less: unamortized debt discount (296 ) (599 ) Plus: accreted value of final payment 517 383 Term loan facility, net $ 6,098 $ 8,798 Future principal payments due under the loan facility are as follows (in thousands): Principal Payments Year ending December 31: 2018 3,423 2019 2,454 Total future principal payments due under loan agreement $ 5,877

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Operating Lease Commitments Rent expense was $0.3 million for each of the years ended December 31, 2017 and 2016. The Company leases 8,894 square feet of office space in Newark, California pursuant to a lease which commenced January 16, 2014 and expires on January 15, 2019. Future minimum lease payments under operating lease commitments are as follows (in thousands): Lease Payments Year ending December 31: 2018 228 Total future minimum payments $ 228 Indemnification In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification, including indemnification associated with product liability or infringement of intellectual property rights. The Company’s exposure under these agreements is unknown because it involves future claims that may be made against the Company that may be, but have not yet been, made. To date, the Company has not paid any claims or been required to defend any action related to these indemnification obligations, and no amounts have been accrued in the accompanying balance sheets related to these indemnification obligations. The Company has agreed to indemnify its officers and directors for losses and costs incurred in connection with certain events or occurrences, including advancing money to cover certain costs, subject to certain limitations. The maximum potential amount of future payments the Company could be required to make under this indemnification is unlimited; however, the Company maintains insurance policies that may limit its exposure and may enable it to recover a portion of any future amounts paid. Assuming the applicability of coverage, the willingness of the insurer to assume coverage, and subject to certain retention, loss limits, and other policy provisions, the Company believes the fair value of these indemnification obligations is not material. Accordingly, the Company has not recognized any liabilities relating to these obligations as of December 31, 2017 and 2016. No assurances can be given that the covering insurers will not attempt to dispute the validity, applicability, or amount of coverage without expensive litigation against these insurers, in which case the Company may incur substantial liabilities as a result of these indemnification obligations.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity The Company is authorized to issue 10,000,000 shares of preferred stock as of December 31, 2017 and 2016, respectively. The Company is authorized to issue 100,000,000 shares of common stock as of December 31, 2017 and 2016, respectively. Common Stock Issuances On February 7, 2017, pursuant to a shelf registration statement on Form S-3, the Company completed the issuance of 5,181,348 shares of its common stock at $1.93 per share which the Company refers to as the February 2017 public offering. Net proceeds to the Company in connection with the February 2017 public offering were approximately $9.2 million after deducting underwriting discounts, commissions and other offering expenses. On July 24, 2017, pursuant to a shelf registration statement on Form S-3, the Company completed the issuance of 14,950,000 shares of our common stock at $6.50 per share, which the Company refers to as the July 2017 public offering. Net proceeds to the Company in connection with the July 2017 public offering were approximately $91.1 million after deducting underwriting discounts, commissions and other offering expenses. On February 1, 2018, pursuant to a new $200 million shelf registration statement on Form S-3, the Company completed the issuance of 13,340,000 shares of its common stock at $10.80 per share, which the Company refers to as the February 2018 public offering. Net proceeds to the in connection with the February 2018 public offering were approximately $135.5 million after deducting underwriting discounts, commissions and other offering expenses. Common Stock Warrants In connection with a 2013 financing and the Company’s private placement of common stock and warrants in September 2013, October 2013 and January 2014, the Company issued five-year warrants to purchase 1,741,788 shares of the Company’s common stock at an exercise price of $5.75 per share (referred to as the 2013 financing warrants). The Company also issued seven-year warrants to purchase 121,739 shares of the Company’s common stock to certain lenders at an exercise price of $5.00 per share in September 2013 and in connection with the 2015 loan facility, the Company issued ten-year warrants to purchase 114,436 shares of its common stock to its lenders at an exercise price of $2.84 per share (referred to as the lender warrants). The 2013 financing warrants contain anti-dilution provisions that are contingent on the occurrence of a major transaction which precludes them from being indexed to the Company’s common stock and also do not meet other criteria for equity classification. Such provisions could also result in the settlement of the 2013 financing warrants for more shares of common stock than the Company has authorized. Due to these provisions, the Company is required to account for the 2013 financing warrants and the lender warrants as liabilities at fair value. As of December 31, 2017 and 2016, the Company’s warrants were measured using Level 3 inputs. During the year, the Company changed its valuation technique and began to value its warrant liability using a Black-Scholes option pricing model, the inputs for which include: the exercise price of the warrants; the market price of the underlying common shares; a risk-free interest rate based on the rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the remaining contractual term of the warrants; an assumed dividend yield of zero based on the Company’s expectation that it will not pay dividends in the foreseeable future; an expected term based on the remaining contractual term of the warrants; and expected volatility based upon the Company’s historical volatility. The significant unobservable input used in measuring the fair value of the common stock warrant liabilities is the expected volatility. Significant increases in volatility would result in a higher fair value measurement. Historically, the Company used a binomial option-pricing model to value its warrant liabilities. The inputs for the binomial model are similar to the Black-Scholes model but also incorporate other more complex inputs that, in the Company’s case, have previously included the expected timing, probability and valuation impact of certain potential strategic events. The significant unobservable inputs used in measuring the fair value of the common stock warrant liabilities under the binomial lattice option-pricing model were expected volatility and the probability and valuation impact of certain potential strategic events. Significant increases in volatility would result in a higher fair value measurement and significant increases in the probability and valuation impact of certain potential strategic events occurring would result in a significantly higher fair value measurement. Management concluded that no potential strategic events were expected to occur that, upon their announcement, could significantly impact the warrant liabilities valuation prior to their expiration beginning in late 2018 and ending in early 2019. These warrants were recorded at fair value upon issuance and were revalued at fair value as of December 31, 2017 and 2016 using a Black-Scholes model and binomial lattice option pricing model, respectively. The resulting increase in fair value of $5.8 million for the year ended December 31, 2017 and decrease in fair value $0.1 million for the year ended December 31, 2016 were recorded as a revaluation loss and gain, respectively, in other income (expense), net in the Company’s statement of operations and comprehensive loss. As of December 31, 2017, 40,250 warrants were exercised for cash proceeds of $0.2 million and 166,193 warrants were cashless exercised. No warrants were exercised for the year ended December 31, 2016. The 2013 financing warrants begin to expire in September 2018 and the lender warrants begin to expire in September 2020. Shares of Common Stock Authorized for Issuance As of December 31, 2017 and December 31, 2016, the Company had reserved shares of authorized but unissued common stock as follows: December 31, December 31, 2017 2016 Common stock warrants 1,460,955 1,667,398 Equity incentive plan 4,021,983 3,456,771 Total reserved shares of common stock 5,482,938 5,124,169

Stock Plan and Stock-Based Comp

Stock Plan and Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Plans and Stock-Based Compensation	9. Stock Plan and Stock-Based Compensation Stock Plan In September 2013, the Company’s stockholders approved the 2013 Equity Incentive Plan (the “2013 Plan”), under which shares of common stock are reserved for the granting of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, performance cash awards and other stock awards by the Company. These awards may be granted to employees, members of the Board of Directors, and consultants. The 2013 Plan has a term of ten years and replaced the 2003 Equity Incentive Plan, which had similar terms. The 2013 Plan permits the Company to (i) grant incentive stock options to directors and employees at not less than 100% of the fair value of common stock on the date of grant; (ii) grant nonqualified options to employees, directors, and consultants at not less than 85% of fair value; (iii) award stock bonuses; and (iv) grant rights to acquire restricted stock at not less than 85% of fair value. Options generally vest over a four year period and have a term of ten years. Options granted to 10% stockholders have a maximum term of five years and require an exercise price equal to at least 110% of the fair value on the date of grant. The exercise price of all options granted to date has been at least equal to the fair value of common stock on the date of grant. The share reserve under the 2013 Plan will automatically increase on January 1 st st st Stock Plan Activity As of December 31, 2017, there were no shares available for grant under the 2013 Plan. In accordance with the provisions of the 2013 Plan, the number of shares available for issuance under the plan automatically increased by 2,220,439 shares on January 1, 2018. The following table summarizes stock option activity: Shares Subject to Outstanding Options Weighted Average Exercise Price of Options Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2015 1,804,083 $ 7.41 Options granted 646,667 1.28 Options exercised — 0 Options forfeited (14,319 ) 4.50 Options expired (42,043 ) 25.01 Outstanding as of December 31, 2016 2,394,388 5.46 Options granted 2,224,801 4.79 Options exercised (472,169 ) 3.40 Options forfeited (82,578 ) 1.91 Options expired (9,001 ) 10.00 Outstanding as of December 31, 2017 4,055,441 $ 5.40 7.28 $ 15,975 Vested and expected to vest as of December 31, 2017 4,055,441 $ 5.40 7.28 $ 15,975 Exercisable as of December 31, 2017 1,973,842 $ 5.69 5.35 $ 7,371 The total intrinsic value of options exercised was $2.5 million for the year ended December 31, 2017. No options were exercised during the year ended December 31, 2016. Vested and Unvested Awards The total fair value of options vested including performance options, was $3.9 million and $2.2 million for the years ended December 31, 2017 and 2016, respectively. As of December 31, 2017, unamortized employee and non-employee stock-based compensation expense of $6.9 million is expected to be recognized over a weighted average period of 2.7 years. Performance Options In July 2016, the Company granted 327,000 performance-based stock options (PSOs) to executives and senior officers. PSOs represent a contingent right to purchase the Company’s common stock upon the achievement of specific conditions. Specifically, these PSOs vest upon the achievement of certain clinical development and capital raising milestones that must occur before December 31, 2016. In December 2016, the PSOs were modified by extending the term by one month to January 31, 2017. The following table summarizes performance option activity: Weighted- Shares Average Subject to Exercise Outstanding Price of Options Options Outstanding as of December 31, 2015 — $ — Options granted 327,000 1.82 Outstanding as of December 31, 2016 327,000 1.82 Options exercised (26,000 ) 1.82 Outstanding as of December 31, 2017 301,000 $ 1.82 Performance options outstanding as of December 31, 2017 had a weighted average remaining contractual term of 5.92 years and an aggregate intrinsic value of $2.2 million. Upon achievement of the clinical development and capital raising milestones, related expense of $192,000 and $199,000 were recognized for years ended December 31, 2017 and 2016, respectively. The modification to extend the term of the PSOs did not have a material impact on the Company’s financial statements. Incentive Awards In December 2013, January 2014, and April 2014, as permitted by the 2013 Plan, the Company issued certain incentive awards to directors, employees and a consultant which are subject to 252,752 shares of the Company’s common stock and are exercisable at a weighted average price of $5.21 per share when vested. The Company may determine at its option whether to settle exercised awards in shares of common stock or in cash. Each recipient’s incentive award defines the number of common shares that may be acquired upon exercise provided the Company chooses to settle in shares. For awards settled in cash, the Company must pay the recipient the excess of the fair market value of the Company’s common stock on the date of exercise over the exercise price paid by the recipient multiplied by the number of shares the recipient would be entitled to receive had the award been settled in shares of the Company’s common stock. Pursuant to their terms, the incentive awards have a term of 10 years and were initially scheduled to vest 100% on the second anniversary of their grant date. However, as a result of the approval by Company’s stockholders of a 500,000 share increase to the 2013 Plan’s share reserve in June 2014, the incentive awards were automatically modified to vest monthly over four years effective from their grant date. The Company is recognizing the value of the incentive awards over the remaining four year vesting period. The Company recorded $334,000 and $272,000 of stock based compensation expense in the years ended December 31, 2017 and 2016, respectively, pertaining to its incentive awards. Incentive awards outstanding totaled 129,776 as of December 31, 2017. Options Granted to Nonemployees The Company has issued options to purchase shares of common stock to certain scientific advisors and consultants. The stock options have various exercise prices, a term of ten years, and vest over periods up to forty-eight months. The Company granted to these advisors and consultants options to purchase 15,000 and 18,000 shares of common stock, in 2017 and 2016, respectively. As of December 31, 2017, options to purchase 21,041 shares of common stock remained unvested, and compensation related to these stock options is subject to remeasurement each reporting period as the shares vest. In 2013, the Company also issued an incentive award for 2,335 shares to a scientific advisor, of which was fully vested as of December 31, 2017. The Company recorded $114,099 and $17,510 of expense in the years ended December 31, 2017 and 2016, respectively, related to these options and awards. Stock-Based Compensation Expense Stock-based compensation expense, net of estimated forfeitures, included in the statements of operations and comprehensive loss is as follows (in thousands): Year Ended December 31, 2017 2016 Research and development $ 1,301 $ 995 General and administrative 3,619 1,478 Total stock-based compensation expense $ 4,920 $ 2,473 Valuation Assumptions The following table presents the weighted-average assumptions the Company used in the Black-Scholes option-pricing model to derive the grant date fair values of stock options and performance-based stock options along with the resulting estimated weighted-average grant date fair values per share: Year Ended December 31, 2017 2016 Expected term Options 6.0 yrs 6.1 yrs Performance options — 5.1 yrs Expected volatility Options 84 % 80 % Performance options — 85 % Risk-free interest rate Options 2.15 % 1.57 % Performance options — 1.56 % Expected dividend yield Options — — Performance options — — Weighted-average grant date fair value per share Options $ 3.36 $ 0.89 Performance options — $ 1.20 Expected Term The Company does not believe it can currently place reliance on its historical exercise and post-vesting termination activity to provide accurate data for estimating the expected term. Therefore, for stock option grants made during the years ended December 31, 2017 and 2016, the Company has opted to use the simplified method for estimating the expected term, which is an average of the contractual term of the options and its ordinary vesting period. The expected term represents the period of time that options are expected to be outstanding. Expected Volatility As the Company has limited trading history for its common stock, the expected stock price volatility for the Company’s common stock was estimated by considering the volatility rates of similar publicly traded peer entities within the life sciences industry. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Risk-Free Interest Rate The risk-free interest rate assumption was based on U.S. Treasury instruments with constant maturities whose term was consistent with the expected term of stock options granted by the Company. Expected Dividend Yield The Company has never declared or paid cash dividends and does not plan to pay cash dividends in the foreseeable future. Consequently, the Company uses an expected dividend yield of zero. Forfeitures Prior to January 1, 2017, the Company recognized stock expense net of estimated forfeitures; however, in connection with the adoption of ASU 2016-09, the Company elected to change its accounting policy to reflect the impact of forfeitures as they occur in 2017. In making this policy change, the Company was required to record a cumulative effect of this change in retained earnings on January 1, 2017 which was not material.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2017
Postemployment Benefits [Abstract]
401(k) Plan	10. 401(k) Plan The Company provides a qualified 401(k) savings plan for its employees. All employees are eligible to participate, provided they meet the requirements of the plan. While the Company may elect to match employee contributions, no such matching contributions have been made through December 31, 2017 and 2016.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes No provision for U.S. income taxes exists due to tax losses incurred in all periods presented. All losses incurred were U.S. based. Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31 2017 2016 Deferred tax assets: Federal and state net operating loss carryforwards $ 63,935 $ 88,111 Capitalized research and development 9,455 22,272 Federal and state tax credit carryforwards 13,529 8,141 Stock based compensation 1,493 2,080 Other 438 974 Total deferred tax assets 88,850 121,578 Valuation allowance (88,850 ) (121,578 ) Net deferred tax assets $ — $ — On December 22, 2017, the U.S. federal government enacted the Tax Cuts and Jobs Act (“the Act”). The Tax Act contains, among other things, significant changes to corporate taxation, including reduction of the corporate tax rate from a top marginal rate of 35% to a flat rate of 21% for tax years beginning after December 31, 2017, limitation of the deduction for net operating losses to 80% of current year taxable income and elimination of net operating loss carrybacks, implementing a territorial tax system, and requiring a mandatory one-time tax on U.S. owned undistributed foreign earnings and profits known as the transition tax. Pursuant to SAB 118, an entity may select between one of three scenarios to determine a reasonable estimate arising from the Tax Act. The scenarios are (i) a final estimate which effectively closes the measurement window; (ii) a reasonable estimate leaving the measurement window open for future revisions; and (iii) no estimate as the law is still being analyzed. The Company was able to provide a reasonable estimate for the revaluation of deferred taxes. As such, the Company has recorded a $38.2 million reduction in deferred tax assets for the revaluation of deferred taxes which was offset by a corresponding decrease to the Company’s full valuation allowance. The ultimate impact of the Act may differ from provision amounts recorded. Adjustments, if any, are not expected to impact to the statement of operations and comprehensive loss due to the full valuation allowance on the Company’s deferred tax assets. Realization of the net deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which is uncertain. Based on the weight of available positive and negative objective evidence, management believes it more likely than not that the Company’s deferred tax assets are not realizable. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. The net valuation allowance decreased by $32.7 million during the year ended December 31, 2017 and increased $9.7 million during the year ended December 31, 2016. The following is a reconciliation of the expected statutory federal income tax provision to the actual income tax provision (in thousands): December 31 2017 2016 Income tax benefit at federal statutory tax rate of 34% $ (9,369 ) $ (9,068 ) Change in valuation allowance (32,709 ) 9,775 Effect of change in enacted tax rates 38,194 - State income taxes, net of federal benefit 5,094 (458 ) Permanent items 4,027 196 Research credits (5,237 ) (445 ) Income tax (benefit) expense $ — $ — Pursuant to Internal Revenue Code (“IRC”), Section 382 and 383, use of the Company’s U.S. federal and state net operating loss and research and development income tax credit carryforwards may be limited in the event of a cumulative change in ownership of more than 50.0% within a three-year period. The Company completed an analysis under IRC Sections 382 and 383 through December 21, 2007 and determined that the Company’s net operating losses and research and development credits were subject to limitations due to changes in ownership through December 31, 2007. The net operating loss carryforwards reflected in the deferred tax assets at December 31, 2017 have been adjusted to reflect Section 382 limitations resulting from that change. The Company has been in a net operating loss position since 2008. The Company has not performed any additional analysis for IRC Sections 382 and 383 and there is a risk that additional changes in ownership could have occurred since December 31, 2007. If a change in ownership were to have occurred, additional net operating loss and tax credit carryforwards could be eliminated or restricted. If eliminated, the related asset would be removed from the deferred tax asset schedule with a corresponding reduction in the valuation allowance. As of December 31, 2017, the Company has federal net operating loss carryforwards of $255.7 million and state net operating loss carryforwards of $146.6 million to offset future taxable income, if any. In addition, the Company has federal research and development tax credit carry forwards of $7.7 million, a federal research and development orphan drug tax credit carry forward of $6.0 million, and state research and development tax credit carryforwards of $4.0 million. If not utilized, the federal net operating loss and tax credit carryforwards will expire beginning in 2024 through 2037 and the state net operating loss carryforwards will expire beginning in 2028 through 2037. Under the Act, federal net operating losses incurred in 2018 and future years may be carried forward indefinitely, but the deductibility of such federal net operating losses is limited. It is uncertain to what extent various states will conform to the Act with regard to net operating loss carry forwards. The state tax credit will carry forward indefinitely. The following table summarizes activity related to the Company’s gross unrecognized tax benefits (in thousands): Total Balances as of December 31, 2015 $ 2,127 Increases related to prior year tax positions — Increases related to 2016 tax positions 159 Balances as of December 31, 2016 $ 2,286 Increases related to prior year tax positions — Increases related to 2017 tax positions 1,009 Balances as of December 31, 2017 $ 3,295 The unrecognized tax benefits, if recognized, would not have an impact on the Company’s effective tax rate assuming the Company continues to maintain a full valuation allowance position. Based on prior year’s operations and experience, the Company does not expect a significant change to its unrecognized tax benefits over the next twelve months. The unrecognized tax benefits may increase or change during the next year for unexpected or unusual items for items that arise in the ordinary course of business. The Company files income tax returns in the U.S. federal and California jurisdiction and is not currently under examination by federal, state, or local taxing authorities for any open tax years. Due to net operating loss carryforwards, all years remain open for income tax examination by tax authorities in the U.S. and states in which the Company files tax returns.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	12. Related-Party Transactions The Company paid a former member of its Board of Directors, who is also a member of its Scientific and Clinical Advisory Boards, a total of $60,000 in each of the years ended December 31, 2017 and 2016 in monthly cash retainers.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events On February 1, 2018, the Company closed an underwritten public offering of its common stock. The Company sold 13,340,000 shares of its common stock in the offering at a public offering price of $10.80 per share before underwriting discounts and commissions, which resulted in net proceeds to the Company of $135.5 million after deducting underwriter’s discounts, commissions and other offering expenses.

Organization and Description 21

Organization and Description of Business (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Liquidity	Liquidity The Company has incurred net operating losses and negative cash flows from operations since its inception. During the year ended December 31, 2017, the Company incurred a net loss of $27.6 million and used $19.6 million of cash in operations. At December 31, 2017, the Company had an accumulated deficit of $450.5 million. CymaBay expects to incur substantial research and development expenses as it continues to study its product candidates in clinical trials. To date, none of the Company’s product candidates have been approved for marketing and sale, and the Company has not recorded any revenue from product sales. As a result, management expects operating losses to continue in future years. The Company’s ability to achieve profitability is dependent primarily on its ability to successfully develop, acquire or in-license additional product candidates, continue clinical trials for product candidates currently in clinical development, obtain regulatory approvals, and support commercialization activities for partnered product candidates. Products developed by the Company will require approval of the U.S. Food and Drug Administration (FDA) or a foreign regulatory authority prior to commercial sale. The regulatory approval process is expensive, time-consuming, and uncertain, and any denial or delay of approval could have a material adverse effect on the Company. Even if approved, the Company’s products may not achieve market acceptance and will face competition from both generic and branded pharmaceutical products. As of December 31, 2017, the Company’s cash, cash equivalents and marketable securities totaled $97.2 million. The Company believes these funds, together with net proceeds of $135.5 million received in the public offering in February 2018, and a $5 million milestone payment received pursuant to the Company’s license agreement with Kowa in January 2018, are sufficient to fund the Company’s current operating plan into 2021.
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP), which requires management to make informed estimates and assumptions that impact the amounts and disclosures reported in the financial statements and accompanying notes. Accounting estimates and assumptions are inherently uncertain. Management bases its estimates on historical experience and on assumptions believed to be reasonable under the circumstances. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Actual results could differ materially from those estimates and assumptions. The Company believes significant judgment is involved in determining and in estimating the valuation of stock-based compensation, accrued clinical expenses, and equity instrument valuations. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. Estimates are assessed each reporting period and updated to reflect current information and any changes in estimates will generally be reflected in the period first identified.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments during the periods reported consist of cash and cash equivalents, marketable securities, accounts receivable, prepaid expenses, other current assets, accounts payable, accrued interest payable, accrued expenses, the facility loan, and warrant liabilities. Fair value estimates of these instruments are made at a specific point in time, based on relevant market information. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment. The carrying amounts of financial instruments such as cash and cash equivalents, accounts receivable, prepaid expenses, other current assets, accounts payable, accrued expenses, and accrued interest payable approximate the related fair values due to the short maturities of these instruments. Based on prevailing borrowing rates available to the Company for loans with similar terms, the Company believes the fair value of the facility loan, considering level 2 inputs, approximates its carrying value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Assets and liabilities that are measured at fair value are reported using a three-level fair value hierarchy that prioritizes the inputs used to measure fair value. This hierarchy maximizes the use of observable inputs and maximizes the use of unobservable inputs and is as follows: Level 1—Quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2—Inputs other than quoted prices in active markets that are observable for the asset or liability, either directly or indirectly. Level 3—Inputs that are significant to the fair value measurement and are unobservable (i.e. supported by little market activity), which requires the reporting entity to develop its own valuation techniques and assumptions. The following tables present the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis using the above input categories (in thousands): As of December 31, 2017 (In thousands) Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 12,822 $ — $ — $ 12,822 Commercial paper — 6,035 — 6,035 Total cash equivalents 12,822 6,035 — 18,857 Short-term investments: Commercial paper — 35,886 — 35,886 Corporate debt securities — 19,760 — 19,760 Asset-backed securities — 11,060 — 11,060 U.S. treasury securities — 7,450 7,450 Total short-term investments — 74,156 — 74,156 Total assets measured at fair value $ 12,822 $ 80,191 $ — $ 93,013 Warrant liability $ — $ — $ 6,091 $ 6,091 Total liabilities measured at fair value $ — $ — $ 6,091 $ 6,091 As of December 31, 2016 (In thousands) Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 9,456 $ — $ — $ 9,456 Commercial paper — 599 — 599 Corporate debt securities — 500 — 500 Total cash equivalents 9,456 1,099 — 10,555 Short-term investments: Commercial paper — 4,295 — 4,295 Corporate debt securities — 2,204 — 2,204 Total short-term investments — 6,499 — 6,499 Total assets measured at fair value $ 9,456 $ 7,598 $ — $ 17,054 Warrant liability $ — $ — $ 1,145 $ 1,145 Total liabilities measured at fair value $ — $ — $ 1,145 $ 1,145 The Company estimates the fair value of its corporate debt, asset backed securities, and U.S. treasury securities by taking into consideration valuations obtained from third-party pricing services. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities, issuer credit spreads; benchmark securities; prepayment/default projections based on historical data; and other observable inputs. There were no transfers between Level 1 and Level 2 during the periods presented. As of December 31, 2017 and 2016, financial instruments measured using Level 3 inputs consisted of the Company’s warrants, which are accounted for as liabilities. During the year, the Company changed its valuation technique and began to value its warrant liability using a Black-Scholes option pricing model, the inputs for which include: exercise price of the warrants, market price of the underlying common shares, dividend yield, expected term, expected volatility, and a risk-free interest rate. Changes to any of these inputs can have a significant impact on the estimated fair value of the warrants. Historically, the Company used a binomial option pricing model to value its warrant liabilities. The inputs for the binomial model are similar to the Black-Scholes model but also incorporate other more complex inputs that, in the Company’s case, have previously included the expected timing, probability and valuation impact of certain potential strategic events. Management concluded that no potential strategic events were expected to occur that, upon their announcement, could significantly impact the warrant liabilities valuation prior to their expiration beginning in late 2018 and ending in early 2019. The following tables set forth a summary of the changes in the fair value of our liabilities measured using Level 3 inputs (in thousands): For the Twelve Months Ended December 31, 2017 2016 Balance, beginning of period $ 1,145 $ 1,220 Issuance of financial instrument — — Change in fair value 5,773 (75 ) Settlement of financial instrument (827 ) — Balance, end of period $ 6,091 $ 1,145
Cash Equivalents and Marketable Securities	Cash, Cash Equivalents, and Marketable Securities The Company considers all highly liquid investments with a remaining maturity of 90 days or less at the time of purchase to be cash equivalents. Cash and cash equivalents consist of deposits with commercial banks in checking, interest-bearing, demand money market accounts, corporate debt securities, and commercial paper. The Company invests excess cash in marketable securities with high credit ratings that are classified in Level 1 and Level 2 of the fair value hierarchy. These securities consist primarily of corporate debt, commercial paper, asset-backed securities, and U.S. treasury securities and are classified as “available-for-sale.” The Company considers marketable securities as short-term investments if the maturity date is less than one year from the balance sheet date. The Company considers marketable securities as long-term investments if the maturity date is in excess of one year of the balance sheet date. Realized gains and losses from the sale of marketable securities, if any, are calculated using the specific-identification method. Realized gains and losses and declines in value judged to be other-than- temporary are included in interest income or expense in the statements of operations and comprehensive loss. Unrealized holding gains and losses are reported in accumulated other comprehensive loss in the balance sheets. To date, the Company has not recorded any impairment charges on its marketable securities related to other-than-temporary declines in market value. In determining whether a decline in market value is other-than-temporary, various factors are considered, including the cause, duration of time and severity of the impairment, any adverse changes in the investees’ financial condition, and the Company’s intent and ability to hold the security for a period of time sufficient to allow for an anticipated recovery in market value.
Concentration of Credit Risk	Concentration of Credit Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to a concentration of credit risk to the extent of the fair value recorded in the balance sheet. The Company invests cash that is not required for immediate operating needs primarily in highly liquid instruments that bear minimal risk. The Company has established guidelines relating to the quality, diversification, and maturities of securities to enable the Company to manage its credit risk. We are exposed to credit risk in the event of a default by the financial institutions holding our cash, cash equivalents and investments and issuers of investments to the extent recorded on the balance sheets. Certain materials and key components that the Company utilizes in its operations are obtained through single suppliers. Since the suppliers of key components and materials must be named in a new drug application (NDA) filed with the U.S. Food and Drug Administration (FDA) for a product, significant delays can occur if the qualification of a new supplier is required. If delivery of material from the Company’s suppliers were interrupted for any reason, the Company may be unable to supply any of its product candidates for clinical trials.
Property and Equipment	Property and Equipment Property and equipment is recorded at cost, less accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method, and the cost is amortized over the estimated useful lives of the respective assets, generally three to seven years. Leasehold improvements are amortized over the shorter of the useful lives or the non-cancelable term of the related lease. Maintenance and repair costs are charged as expense in the statements of operations and comprehensive loss as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss is recognized if the estimated undiscounted future cash flow expected to result from the use and eventual disposition of an asset is less than the carrying amount. While the Company’s current and historical operating losses and cash flows are indicators of impairment, the Company believes the future cash flows to be received support the carrying value of its long-lived assets. Accordingly, the Company has not recognized any impairment losses as of December 31, 2017.
Deferred Rent	Deferred Rent The Company records its costs under facility operating lease agreements as rent expense. Rent expense is recognized on a straight-line basis over the non-cancelable term of the operating lease. The difference between the actual amounts paid and amounts recorded as rent expense is recorded as deferred rent in the accompanying balance sheets.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred or services have been rendered, (iii) the price is fixed or determinable, and (iv) collectability is reasonably assured. Payments received in advance of work performed are recorded as deferred revenue and recognized when earned. Collaboration and license agreements may include non-refundable upfront license fees, contingent consideration payments based on the achievement of defined collaboration objectives and royalties on sales of commercialized products. The Company’s performance obligations under collaboration and license agreements may include the license or transfer of intellectual property rights, obligations to provide research and development services and related materials and obligations to participate on certain development and/or commercialization committees with the collaborators. If the Company determines that multiple deliverables in an arrangement exist, the consideration is allocated to one or more units of accounting based upon the relative-selling-price of each element in an arrangement. The relative-selling-price used for each deliverable is based on vendor-specific objective evidence, if available, third-party evidence if vendor-specific objective evidence is not available, or estimated selling price if neither vendor-specific or third-party evidence is available. The Company identifies deliverables at the inception of the arrangement. Each deliverable is accounted for as a separate unit of accounting if both of the following criteria are met: (1) the delivered item or items have value to the customer on a standalone basis and (2) for an arrangement that includes a general right of return relative to the delivered items, delivery or performance of the undelivered items is considered probable and substantially in the Company’s control. Non-refundable upfront payments received and allocated to separate units of accounting are recognized as revenue when the four basic revenue recognition criteria are met for each unit of accounting. The Company recognizes payments that are contingent upon achievement of a substantive milestone in their entirety in the period in which the milestone is achieved. Milestones are defined as events that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones subject to this guidance. Further, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables and payment terms within the agreement and commensurate with the Company’s performance to achieve the milestone after commencement of the agreement. Any contingent payment that becomes payable upon achievement of events that are not considered substantive milestones are allocated to the units of accounting previously identified at the inception of an arrangement when the contingent payment is received and revenue is recognized based on the revenue recognition criteria for each unit of accounting.
Research and Development Expenses	Research and Development Expenses Research and development expenses consist of costs incurred in identifying, developing, and testing product candidates. These expenses consist primarily of costs for research and development personnel, including related stock-based compensation; contract research organizations (CRO) and other third parties that assist in managing, monitoring, and analyzing clinical trials; investigator and site fees; laboratory services; consultants; contract manufacturing services; non-clinical studies, including materials; and allocated expenses, such as depreciation of assets, and facilities and information technology that support research and development activities. Research and development costs are expensed as incurred, including expenses that may or may not be reimbursed under research and development funding arrangements. Payments made prior to the receipt of goods or services to be used in research and development are recorded as prepaid assets until the goods are received or services are rendered. Such payments are evaluated for current or long term classification based on when they will be realized. The Company records expenses related to clinical studies and manufacturing development activities based on its estimates of the services received and efforts expended pursuant to contracts with multiple CROs and manufacturing vendors that conduct and manage these activities on its behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract, and may result in uneven payment flows. There may be instances in which payments made to the Company’s vendors will exceed the level of services provided and result in a prepayment of the expense. Payments under some of these contracts depend on factors such as the successful enrollment of subjects and the completion of clinical trial milestones. In amortizing or accruing service fees, the Company estimates the time period over which services will be performed, enrollment of subjects, number of sites activated and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the Company will adjust the accrued or prepaid expense balance accordingly. To date, there have been no material differences from the Company’s estimates to the amounts actually incurred.
Stock-Based Compensation	Stock-Based Compensation Employee and director stock-based compensation is measured at fair value on the grant date of the award. Compensation cost is recognized as expense on a straight-line basis over the vesting period for options and on an accelerated basis for stock options with performance conditions, net of estimated forfeitures. For stock options with performance conditions, the Company evaluates the probability of achieving performance conditions at each reporting date. The Company begins to recognize the expense when it is deemed probable that the performance conditions will be met. The Company uses the Black-Scholes option pricing model to determine the fair value of stock option awards. The determination of fair value for stock-based awards using an option-pricing model requires management to make certain assumptions regarding subjective input variables such as expected term, dividends, volatility and risk-free rate. The Company is also required to make estimates as to the probability of achieving the specific performance criteria. If actual results are not consistent with the Company’s assumptions and judgments used in making these estimates, the Company may be required to increase or decrease compensation expense, which could be material to the Company’s results of operations. Equity awards granted to non-employees are valued using the Black-Scholes option pricing model. Stock-based compensation expense for nonemployee services is subject to remeasurement as the underlying equity instruments vest and is recognized as an expense over the period during which services are received.
Common Stock Warrant Liabilities	Common Stock Warrant Liabilities The Company’s outstanding common stock warrants issued in connection with certain equity and debt financings that occurred in 2013 through 2015 are classified as liabilities in the accompanying balance sheets because of certain contractual terms that preclude equity classification. The Company estimates the fair value of common stock warrants at each reporting period until the earlier of the exercise of the warrants, at which time the liability will be revalued and reclassified to stockholders’ equity, or expiration of the warrants. The determination of fair value of these common stock warrants requires management to make certain assumptions regarding subjective input variables such as timing, probability and valuation impact of certain potential strategic events, expected term, dividends, expected volatility and risk-free interest rates. If actual results are not consistent with the Company’s assumptions and judgments used in making these estimates, the Company may be required to increase or decrease other (expense) income, net, which could be material to the Company’s results of operations.
Income Taxes	Income Taxes The Company utilizes the liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on differences between the financial reporting and the tax bases of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. A valuation allowance is recorded when it is more likely than not that all or part of a deferred tax asset will not be realized. When the Company establishes or reduces the valuation allowance related to the deferred tax assets, the provision for income taxes will increase or decrease, respectively, in the period such determination is made. The accounting guidance for uncertainty in income taxes prescribes a recognition threshold and measurement attribute criteria for the financial 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 based on the technical merits of the position. The Company is required to file federal and state income tax returns in the United States. The preparation of these income tax returns requires the Company to interpret the applicable tax laws and regulations in effect that could affect the amount of tax paid to these jurisdictions. In December 2017, Securities and Exchange Commission (“SEC”) staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act The Company records interest related to income tax reserves, if any, as interest expense, and any penalties would be recorded as other expense in the statements of operations and comprehensive loss. There was no interest or penalties related to income tax reserves during the years ended December 31, 2017 and 2016.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and net unrealized gains and losses on marketable securities, which are presented in a single continuous statement. Comprehensive loss is disclosed in the statements of stockholders’ equity, and is stated net of related tax effects, if any.
Net Income (Loss) Per Common Share	Net Income (Loss) Per Common Share Basic net loss per share of common stock is based on the weighted average number of shares of common stock outstanding equivalents during the period. Diluted net loss per share of common stock is calculated as the weighted average number of shares of common stock outstanding adjusted to include the assumed exercises of stock options and common stock warrants, if dilutive. The calculation of diluted loss per share also requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the common stock warrants and the presumed exercise of such securities are dilutive to earnings (loss) per share for the period, adjustments to net income or net loss used in the calculation are required to remove the change in fair value of the common stock warrant liability for the period. Likewise, adjustments to the denominator are required to reflect the related dilutive shares. In all periods presented, the Company’s outstanding stock options were excluded from the calculation of net loss per share because the effect would be antidilutive. The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share amounts): Year Ended December 31, 2017 2016 Numerator: Net loss allocated to common stock—basic $ (27,557 ) $ (26,671 ) Adjustment for revaluation of warrants — — Net loss allocated to common stock—diluted $ (27,557 ) $ (26,671 ) Denominator: Weighted average number of common stock shares outstanding - basic 34,903,960 23,447,003 Dilutive common stock warrants — — Weighted average number of common stock shares outstanding - diluted 34,903,960 23,447,003 Net loss per share—basic $ (0.79 ) $ (1.14 ) Net loss per share—diluted $ (0.79 ) $ (1.14 ) The following table shows the total outstanding securities considered anti-dilutive and therefore excluded from the computation of diluted net loss per share (in thousands): Year Ended December 31, 2017 2016 Common stock warrants 1,461 1,667 Common stock options 4,055 2,394 Performance-based stock options 301 327 Incentive awards 130 239 5,947 4,627
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting Standards Update 2014-09 In May 2014, the FASB issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers and related amendments. Subsequently, the Financial Accounting Standards Board (“the FASB”) issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; and ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients. This guidance outlines a new, and single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes nearly all of the existing revenue recognition guidance, including industry-specific guidance. This new revenue recognition model provides a five-step analysis in determining when and how revenue is recognized. The new model will require revenue recognition to depict the transfer of promised goods or services to customers in an amount that reflects the consideration a company expects to receive in exchange for those goods or services. The new revenue standard permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). The Company plans to adopt the new revenue standard in the first quarter of 2018 using the modified retrospective method. To date, the Company’s revenues have been derived from license and collaboration agreements. The consideration that the Company is eligible to receive under such agreements includes upfront payments, milestone payments, and royalties. The Company has assessed its contracts with customers under the five-step process and analyzed such contracts to determine the differences in the accounting treatment under the new revenue standard compared to that of the current accounting standard. The new revenue standard differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments and royalties. The Company has substantially completed its assessment of the new revenue standard for the accounting of its license and collaboration agreements and related financial statement disclosures. The impact of adopting the new revenue standard will not be material and the Company does not expect to record any cumulative-effect adjustment to accumulated deficit upon adoption. The new standard will require more robust disclosures than required by previous guidance, including disclosures related to disaggregation of revenue, discussion of performance obligations, estimates of variable consideration, the judgments made in revenue recognition determinations, adjustments to revenue which relate to activities from previous periods, any significant reversals of revenue, and costs to obtain or fulfill contracts. Accounting Standards Update 2016-02 In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The new standard requires the recognition of assets and liabilities arising from lease transactions on the balance sheet and the disclosure of key information about leasing arrangements. Accordingly, a lessee will recognize a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. Both the asset and liability will initially be measured at the present value of the future minimum lease payments over the lease term. Subsequent measurement, including the presentation of expenses and cash flows, will depend on the classification of the lease as either a finance or an operating lease. Initial costs directly attributable to negotiating and arranging the lease will be included in the asset. Lessees will also be required to provide additional qualitative and quantitative disclosures regarding the amount, timing and uncertainty of cash flows arising from leases. The new standard is effective for fiscal years beginning after December 15, 2018, and interim periods therein. Early adoption is permitted. The Company is currently evaluating the impact this guidance will have on its financial statements. Accounting Standards Update 2016-09 In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting Accounting Standards Update 2017-09 In May 2017, FASB issued ASU No. 2017-09, Compensation-Stock Compensation (Topic 718) - Scope of Modification Accounting Accounting Standards Update 2017-11 In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share Distinguishing Liabilities from Equity Derivatives and Hedging

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	The following tables present the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis using the above input categories (in thousands): As of December 31, 2017 (In thousands) Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 12,822 $ — $ — $ 12,822 Commercial paper — 6,035 — 6,035 Total cash equivalents 12,822 6,035 — 18,857 Short-term investments: Commercial paper — 35,886 — 35,886 Corporate debt securities — 19,760 — 19,760 Asset-backed securities — 11,060 — 11,060 U.S. treasury securities — 7,450 7,450 Total short-term investments — 74,156 — 74,156 Total assets measured at fair value $ 12,822 $ 80,191 $ — $ 93,013 Warrant liability $ — $ — $ 6,091 $ 6,091 Total liabilities measured at fair value $ — $ — $ 6,091 $ 6,091 As of December 31, 2016 (In thousands) Description Level 1 Level 2 Level 3 Fair Value Cash equivalents: Money market funds $ 9,456 $ — $ — $ 9,456 Commercial paper — 599 — 599 Corporate debt securities — 500 — 500 Total cash equivalents 9,456 1,099 — 10,555 Short-term investments: Commercial paper — 4,295 — 4,295 Corporate debt securities — 2,204 — 2,204 Total short-term investments — 6,499 — 6,499 Total assets measured at fair value $ 9,456 $ 7,598 $ — $ 17,054 Warrant liability $ — $ — $ 1,145 $ 1,145 Total liabilities measured at fair value $ — $ — $ 1,145 $ 1,145
Schedule of Changes in Fair Value of Liabilities	The following tables set forth a summary of the changes in the fair value of our liabilities measured using Level 3 inputs (in thousands): For the Twelve Months Ended December 31, 2017 2016 Balance, beginning of period $ 1,145 $ 1,220 Issuance of financial instrument — — Change in fair value 5,773 (75 ) Settlement of financial instrument (827 ) — Balance, end of period $ 6,091 $ 1,145
Computation of Basic and Diluted Net Loss per Share	The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share amounts): Year Ended December 31, 2017 2016 Numerator: Net loss allocated to common stock—basic $ (27,557 ) $ (26,671 ) Adjustment for revaluation of warrants — — Net loss allocated to common stock—diluted $ (27,557 ) $ (26,671 ) Denominator: Weighted average number of common stock shares outstanding - basic 34,903,960 23,447,003 Dilutive common stock warrants — — Weighted average number of common stock shares outstanding - diluted 34,903,960 23,447,003 Net loss per share—basic $ (0.79 ) $ (1.14 ) Net loss per share—diluted $ (0.79 ) $ (1.14 )
Anti-Dilutive Securities Excluded from the Computation of Diluted Net Loss per Share	The following table shows the total outstanding securities considered anti-dilutive and therefore excluded from the computation of diluted net loss per share (in thousands): Year Ended December 31, 2017 2016 Common stock warrants 1,461 1,667 Common stock options 4,055 2,394 Performance-based stock options 301 327 Incentive awards 130 239 5,947 4,627

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Cash And Cash Equivalents [Abstract]
Marketable Available-for-Sale Securities	Marketable available-for-sale securities as of December 31, 2017 and 2016 consist of the following (in thousands): Gross Gross Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value As of December 31, 2017: Commercial paper 35,886 — — 35,886 Corporate debt securities 19,785 — (25 ) 19,760 Asset-backed securities 11,070 — (10 ) 11,060 U.S. treasury securities 7,459 — (9 ) 7,450 $ 74,200 $ — $ (44 ) $ 74,156 Gross Gross Amortized Unrealized Unrealized Estimated Cost Gains Losses Fair Value As of December 31, 2016: Commercial paper 4,295 — — 4,295 Corporate debt securities 2,205 — (1 ) 2,204 $ 6,500 $ — $ (1 ) $ 6,499

Certain Balance Sheet Items (Ta

Certain Balance Sheet Items (Tables)	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Property and Equipment	Property and equipment consist of the following (in thousands): December 31, December 31, 2017 2016 Office and computer equipment $ 177 $ 177 Purchased software 83 83 Furniture and fixtures 65 38 Leasehold improvements 65 65 Total 390 363 Less accumulated depreciation and amortization (321 ) (286 ) Property and equipment, net $ 69 $ 77
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): December 31, December 31, 2017 2016 Accrued compensation $ 2,416 $ 1,839 Accrued pre-clinical and clinical trial expenses 2,929 1,623 Accrued professional fees 288 982 Other accruals 124 57 Total accrued liabilities $ 5,757 $ 4,501

Facility Loans (Tables)

Facility Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Term Loan Facility, Debt Discounts and Final Payment	The term loan facility, debt discounts and final payment balances as of December 31, 2017 and 2016 are as follows (in thousands): December 31, 2017 2016 Principal payments due under the loan facility $ 5,877 $ 9,014 Less: unamortized debt discount (296 ) (599 ) Plus: accreted value of final payment 517 383 Term loan facility, net $ 6,098 $ 8,798
Schedule of Future Principal Payments Due under Loan Facility	Future principal payments due under the loan facility are as follows (in thousands): Principal Payments Year ending December 31: 2018 3,423 2019 2,454 Total future principal payments due under loan agreement $ 5,877

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Lease Payments	Future minimum lease payments under operating lease commitments are as follows (in thousands): Lease Payments Year ending December 31: 2018 228 Total future minimum payments $ 228

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Reserved Shares of Authorized but Unissued Common Stock	As of December 31, 2017 and December 31, 2016, the Company had reserved shares of authorized but unissued common stock as follows: December 31, December 31, 2017 2016 Common stock warrants 1,460,955 1,667,398 Equity incentive plan 4,021,983 3,456,771 Total reserved shares of common stock 5,482,938 5,124,169

Stock Plan and Stock-Based Co28

Stock Plan and Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Stock Option Activity	The following table summarizes stock option activity: Shares Subject to Outstanding Options Weighted Average Exercise Price of Options Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2015 1,804,083 $ 7.41 Options granted 646,667 1.28 Options exercised — 0 Options forfeited (14,319 ) 4.50 Options expired (42,043 ) 25.01 Outstanding as of December 31, 2016 2,394,388 5.46 Options granted 2,224,801 4.79 Options exercised (472,169 ) 3.40 Options forfeited (82,578 ) 1.91 Options expired (9,001 ) 10.00 Outstanding as of December 31, 2017 4,055,441 $ 5.40 7.28 $ 15,975 Vested and expected to vest as of December 31, 2017 4,055,441 $ 5.40 7.28 $ 15,975 Exercisable as of December 31, 2017 1,973,842 $ 5.69 5.35 $ 7,371
Summary of Stock-Based Compensation Expense, Net of Estimated Forfeitures	Stock-based compensation expense, net of estimated forfeitures, included in the statements of operations and comprehensive loss is as follows (in thousands): Year Ended December 31, 2017 2016 Research and development $ 1,301 $ 995 General and administrative 3,619 1,478 Total stock-based compensation expense $ 4,920 $ 2,473
Estimated Weighted-Average Grant Date Fair Value	The following table presents the weighted-average assumptions the Company used in the Black-Scholes option-pricing model to derive the grant date fair values of stock options and performance-based stock options along with the resulting estimated weighted-average grant date fair values per share: Year Ended December 31, 2017 2016 Expected term Options 6.0 yrs 6.1 yrs Performance options — 5.1 yrs Expected volatility Options 84 % 80 % Performance options — 85 % Risk-free interest rate Options 2.15 % 1.57 % Performance options — 1.56 % Expected dividend yield Options — — Performance options — — Weighted-average grant date fair value per share Options $ 3.36 $ 0.89 Performance options — $ 1.20
Performance Option [Member]
Summary of Stock Option Activity	The following table summarizes performance option activity: Weighted- Shares Average Subject to Exercise Outstanding Price of Options Options Outstanding as of December 31, 2015 — $ — Options granted 327,000 1.82 Outstanding as of December 31, 2016 327,000 1.82 Options exercised (26,000 ) 1.82 Outstanding as of December 31, 2017 301,000 $ 1.82

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Components of Deferred Tax Assets	Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31 2017 2016 Deferred tax assets: Federal and state net operating loss carryforwards $ 63,935 $ 88,111 Capitalized research and development 9,455 22,272 Federal and state tax credit carryforwards 13,529 8,141 Stock based compensation 1,493 2,080 Other 438 974 Total deferred tax assets 88,850 121,578 Valuation allowance (88,850 ) (121,578 ) Net deferred tax assets $ — $ —
Summary of Reconciliation of Expected Statutory Federal Income Tax Provision to Actual Income Tax Provision	The following is a reconciliation of the expected statutory federal income tax provision to the actual income tax provision (in thousands): December 31 2017 2016 Income tax benefit at federal statutory tax rate of 34% $ (9,369 ) $ (9,068 ) Change in valuation allowance (32,709 ) 9,775 Effect of change in enacted tax rates 38,194 - State income taxes, net of federal benefit 5,094 (458 ) Permanent items 4,027 196 Research credits (5,237 ) (445 ) Income tax (benefit) expense $ — $ —
Summary of Gross Unrecognized Tax Benefits	The following table summarizes activity related to the Company’s gross unrecognized tax benefits (in thousands): Total Balances as of December 31, 2015 $ 2,127 Increases related to prior year tax positions — Increases related to 2016 tax positions 159 Balances as of December 31, 2016 $ 2,286 Increases related to prior year tax positions — Increases related to 2017 tax positions 1,009 Balances as of December 31, 2017 $ 3,295

Organization and Description 30

Organization and Description of Business - Additional Information (Detail) $ in Thousands	Feb. 01, 2018USD ($)	Jul. 24, 2017USD ($)	Feb. 07, 2017USD ($)	Feb. 28, 2018USD ($)	Jan. 31, 2018USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)
Organization and Description of Business [Line Items]
Number of operating segments | Segment							1
Net loss							$ (27,557)	$ (26,671)
Cash flows from operating activities							(19,632)	(23,353)
Accumulated deficit							(450,516)	$ (422,959)
Cash and cash equivalents and marketable securities							$ 97,200
Net proceeds from public offering		$ 91,100	$ 9,200
Subsequent Event [Member]
Organization and Description of Business [Line Items]
Net proceeds from public offering	$ 135,500			$ 135,500
Kowa Pharmaceuticals America Inc [Member]
Organization and Description of Business [Line Items]
Milestone payment received						$ 5,000
Kowa Pharmaceuticals America Inc [Member] | Subsequent Event [Member]
Organization and Description of Business [Line Items]
Milestone payment received					$ 5,000

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 93,013	$ 17,054
Total liabilities measured at fair value	6,091	1,145
Warrant Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value	6,091	1,145
Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	18,857	10,555
Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	12,822	9,456
Cash Equivalents [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	6,035	599
Cash Equivalents [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value		500
Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	74,156	6,499
Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	35,886	4,295
Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	19,760	2,204
Short-term Investments [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	11,060
Short-term Investments [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	7,450
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	12,822	9,456
Level 1 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	12,822	9,456
Level 1 [Member] | Cash Equivalents [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	12,822	9,456
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	80,191	7,598
Level 2 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	6,035	1,099
Level 2 [Member] | Cash Equivalents [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	6,035	599
Level 2 [Member] | Cash Equivalents [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value		500
Level 2 [Member] | Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	74,156	6,499
Level 2 [Member] | Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	35,886	4,295
Level 2 [Member] | Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	19,760	2,204
Level 2 [Member] | Short-term Investments [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	11,060
Level 2 [Member] | Short-term Investments [Member] | U.S. Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	7,450
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value	6,091	1,145
Level 3 [Member] | Warrant Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value	$ 6,091	$ 1,145

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Schedule of Changes in Fair Value of Liabilities (Detail) - Level 3 [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Instruments Classified in Shareholders' Equity Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 1,145	$ 1,220
Change in fair value	5,773	(75)
Settlement of financial instrument	(827)
Balance, end of period	$ 6,091	$ 1,145

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Product Information [Line Items]
Cash and cash equivalents, maturity description	90 days or less
Impairment losses	$ 0
Interest or penalties related to income taxes	$ 0	$ 0
Maximum [Member]
Product Information [Line Items]
Short-term contractual maturities	1 year
Property and equipment, estimated useful lives	7 years
Minimum [Member]
Product Information [Line Items]
Long-term contractual maturities	1 year
Property and equipment, estimated useful lives	3 years

Summary of Significant Accoun34

Summary of Significant Accounting Policies - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss allocated to common stock—basic	$ (27,557)	$ (26,671)
Net loss allocated to common stock—diluted	$ (27,557)	$ (26,671)
Denominator:
Weighted average number of common stock shares outstanding - basic	34,903,960	23,447,003
Weighted average number of common stock shares outstanding - diluted	34,903,960	23,447,003
Net loss per share—basic	$ (0.79)	$ (1.14)
Net loss per share—diluted	$ (0.79)	$ (1.14)

Summary of Significant Accoun35

Summary of Significant Accounting Policies - Anti-Dilutive Securities Excluded from the Computation of Diluted Net Loss per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted loss per share	5,947	4,627
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted loss per share	1,461	1,667
Common Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted loss per share	4,055	2,394
Performance Based Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted loss per share	301	327
Incentive Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted loss per share	130	239

Marketable Securities - Marketa

Marketable Securities - Marketable Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 74,200	$ 6,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(44)	(1)
Estimated Fair Value	74,156	6,499
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,886	4,295
Gross Unrealized Gains	0	0
Estimated Fair Value	35,886	4,295
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,785	2,205
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(25)	(1)
Estimated Fair Value	19,760	$ 2,204
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,070
Gross Unrealized Gains	0
Gross Unrealized Losses	(10)
Estimated Fair Value	11,060
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,459
Gross Unrealized Gains	0
Gross Unrealized Losses	(9)
Estimated Fair Value	$ 7,450

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Asset-backed Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities contractual maturities	1 year	1 year
Commercial Paper [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities contractual maturities	1 year	1 year
Corporate Debt Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities contractual maturities	1 year	1 year
U.S. Treasury Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable securities contractual maturities	1 year	1 year
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Realized gains and losses	$ 0	$ 0
Marketable investments continuous unrealized loss position	$ 0	$ 0

Certain Balance Sheet Items - P

Certain Balance Sheet Items - Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 390	$ 363
Less accumulated depreciation and amortization	(321)	(286)
Property and equipment, net	69	77
Office and Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	177	177
Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	83	83
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	65	38
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 65	$ 65

Certain Balance Sheet Items - A

Certain Balance Sheet Items - Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Accrued compensation	$ 2,416	$ 1,839
Accrued pre-clinical and clinical trial expenses	2,929	1,623
Accrued professional fees	288	982
Other accruals	124	57
Total accrued liabilities	$ 5,757	$ 4,501

Collaboration and License Agr40

Collaboration and License Agreements - Additional Information (Detail)	Dec. 30, 2016USD ($)	Jun. 30, 2010Agreement	Jun. 30, 2006	Jun. 30, 1998USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue						$ 4,800,000	$ 10,000,000
Receivable from collaboration					$ 5,000,000		5,000,000
Pharmacokinetics of Arhalofenate [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue					5,000,000
Receivable from collaboration					5,000,000		5,000,000
Arhalofenate [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue					200,000
Kowa Pharmaceuticals America Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable up-front payment	$ 5,000,000
Upfront consideration paid						$ 5,000,000
Amounts recognized as collaboration revenue for remaining contingent payments							0
Kowa Pharmaceuticals America Inc [Member] | Pharmacokinetics of Arhalofenate [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments	5,000,000
Kowa Pharmaceuticals America Inc [Member] | Achievement of Other Specific Development and Sales [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments	190,000,000
Kowa Pharmaceuticals America Inc [Member] | Phase 3 Study [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments	$ 5,000,000
Janssen Pharmaceutical NV [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of royalty on net sales			8.00%
Janssen Pharmaceuticals, Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of development and license agreements | Agreement		2
Royalty payment							0	$ 0
Accrued royalties					$ 0		0	0
DiaTex, Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty payment							0	0
Monthly license fees				$ 2,000
Potential future development payments				$ 800,000
Development payment							$ 0	$ 0

Facility Loans - Additional Inf

Facility Loans - Additional Information (Detail) - USD ($)	Aug. 07, 2015	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Issued warrants to purchase common stock				114,436
Exercise price of common stock				$ 2.84
Warrant term				10 years
Warrants [Member]
Debt Instrument [Line Items]
Fair value of warrant liabilities		$ 300,000	$ 300,000
Warrants, Exercise Price of $5.00 Per Share [Member]
Debt Instrument [Line Items]
Issued warrants to purchase common stock		121,739	121,739
Exercise price of common stock		$ 5	$ 5
Warrant term			7 years
Second Tranche [Member]
Debt Instrument [Line Items]
Facility loan, unused amount expired					$ 5,000,000
2013 Term Loan Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 10,000,000	$ 10,000,000
Retiring of existing debt	$ 4,100,000
2013 Term Loan Facility [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Facility loan, drawn		$ 5,000,000
Facility loan, fixed interest rate		8.75%	8.75%
Facility loan, interest amortization period		36 months
Facility loan, final interest payment		$ 300,000	$ 300,000
2013 Term Loan Facility [Member] | Second Tranche [Member]
Debt Instrument [Line Items]
Facility loan available for draw down		$ 5,000,000	$ 5,000,000
2015 Term Loan Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 15,000,000
Facility loan, fixed interest rate	8.77%
Debt instrument payment terms				The Company is required to make 12 monthly interest only payments after the funding date followed by a repayment schedule equal to 36 equal monthly payments of interest and principal.
Percentage of principal amount as final payment	6.50%
Facility fee	1.00%
2015 Term Loan Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Present value of the future cash flows	10.00%
2015 Term Loan Facility [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Facility loan, drawn	$ 10,000,000
2015 Term Loan Facility [Member] | Second Tranche [Member]
Debt Instrument [Line Items]
Facility loan available for draw down	$ 5,000,000

Facility Loans - Schedule of Te

Facility Loans - Schedule of Term Loan Facility, Debt Discounts and Final Payment (Detail) - 2015 Term Loan Facility [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Principal payments due under the loan facility	$ 5,877	$ 9,014
Less: unamortized debt discount	(296)	(599)
Plus: accreted value of final payment	517	383
Term loan facility, net	$ 6,098	$ 8,798

Facility Loans - Schedule of Fu

Facility Loans - Schedule of Future Principal Payments Due under Loan Facility (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Maturities Of Long Term Debt [Abstract]
2,018	$ 3,423
2,019	2,454
Total future principal payments due under loan agreement	$ 5,877

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Nov. 08, 2013ft²	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Rent expenses		$ 300,000	$ 300,000
Indemnification liabilities		0	$ 0
Accrued in the consolidated balance sheets related to indemnification obligations		$ 0
Lease Facility [Member]
Loss Contingencies [Line Items]
Area of office space | ft²	8,894
Lease start date	Jan. 16, 2014
Lease expiration date	Jan. 15, 2019

Commitments and Contingencies45

Commitments and Contingencies - Future Minimum Lease Payments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 228
Total future minimum payments	$ 228

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Feb. 01, 2018	Jul. 24, 2017	Feb. 07, 2017	Feb. 28, 2018	Sep. 30, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013
Class of Stock [Line Items]
Preferred stock, shares authorized						10,000,000	10,000,000
Common stock, shares authorized						100,000,000	100,000,000
Common stock, shares issued		14,950,000	5,181,348			44,408,796	23,447,003
Common stock offering price		$ 6.50	$ 1.93
Net proceeds from public offering		$ 91,100,000	$ 9,200,000
Issued warrants to purchase common stock						114,436
Exercise price of common stock						$ 2.84
Warrant term						10 years
Change in fair value of warrant liability						$ 5,773,000	$ (75,000)
Warrants exercised						40,250	0
Proceeds from warrant exercised						$ 231,000
Cashless warrants exercised						166,193
Financing warrants expiration month and year						2018-09
Lender warrants expiration month and year						2020-09
Warrants, Exercise price of $5.75 per share [Member]
Class of Stock [Line Items]
Issued warrants to purchase common stock								1,741,788
Exercise price of common stock								$ 5.75
Warrant term								5 years
Warrants, Exercise Price of $5.00 Per Share [Member]
Class of Stock [Line Items]
Issued warrants to purchase common stock					121,739
Exercise price of common stock					$ 5
Warrant term					7 years
Warrants, Exercise Price of $2.84 Per Share [Member]
Class of Stock [Line Items]
Common stock, shares issued						114,436
Exercise price of common stock						$ 2.84
Warrant term						10 years
Subsequent Event [Member]
Class of Stock [Line Items]
Common stock, shares issued	13,340,000
Common stock offering price	$ 10.80
Net proceeds from public offering	$ 135,500,000			$ 135,500,000
Registration filed on Form S-3	$ 200,000,000

Stockholder's Equity - Reserved

Stockholder's Equity - Reserved Shares of Authorized but Unissued Common Stock (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Total reserved shares of common stock	5,482,938	5,124,169
Common Stock Warrants [Member]
Class of Stock [Line Items]
Total reserved shares of common stock	1,460,955	1,667,398
Equity Incentive Plan [Member]
Class of Stock [Line Items]
Total reserved shares of common stock	4,021,983	3,456,771

Stock Plan and Stock-Based Co48

Stock Plan and Stock-Based Compensation - Additional Information (Detail) - USD ($)	Jan. 01, 2018	Jul. 31, 2016	Sep. 30, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013	Dec. 31, 2007	Dec. 31, 2015	Jun. 30, 2014	Apr. 30, 2014	Jan. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised				$ 2,500,000	$ 0
Fair value of options vested				3,900,000	$ 2,200,000
Unamortized employee and non-employee stock-based compensation expense				$ 6,900,000
Unamortized employee and non-employee stock-based compensation expense recognized period				2 years 8 months 12 days
Number of option granted to employees				2,224,801	646,667
Options outstanding weighted average remaining contractual term				7 years 3 months 10 days
Options outstanding aggregate intrinsic value				$ 15,975,000
Clinical development expense recognized				$ 192,000	$ 199,000
Share reserved for issue				5,482,938	5,124,169
Stock-based compensation expense				$ 4,920,000	$ 2,473,000
Stock options outstanding				4,055,441	2,394,388			1,804,083
Issued warrants to purchase common stock				114,436
Performance Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of option granted to employees					327,000
Options outstanding weighted average remaining contractual term				5 years 11 months 1 day
Options outstanding aggregate intrinsic value				$ 2,200,000
Stock options outstanding				301,000	327,000
Performance Option [Member] | Executives and Senior Officers [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of option granted to employees		327,000
Scientific Advisors and Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, expiration period				10 years
Share based compensation arrangement by share based payment award, award vesting period				48 months
Stock-based compensation expense				$ 114,099	$ 17,510
Issued warrants to purchase common stock				15,000	18,000
Options to purchase common stock, unvested				21,041
Incentive award issued				2,335
Incentive awards outstanding, vested				2,335
2013 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, expiration period			10 years
Share based compensation arrangement percentage increase in share reserved			5.00%
Shares available for grant				0
2013 Equity Incentive Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased in shares available for issuance	2,220,439
2013 Equity Incentive Plan [Member] | Incentive Stock Options for Employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, exercise price percentage			100.00%
2013 Equity Incentive Plan [Member] | Nonqualified Options to Employees, Directors and Consultants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, exercise price percentage			85.00%
2013 Equity Incentive Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, exercise price percentage			85.00%
Share based compensation arrangement by share based payment award, award vesting period			4 years
2013 Equity Incentive Plan [Member] | Stock Options to 10% Stockholders [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, exercise price percentage							110.00%
Share based compensation arrangement by share based payment award, award vesting period							5 years
Incentive Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, expiration period						10 years
Share based compensation arrangement by share based payment award, award vesting period						4 years
Share reserved for issue						252,752			500,000	252,752	252,752
Exercisable weighted average price per share						$ 5.21				$ 5.21	$ 5.21
Stock option plan, Description				Vest monthly over four years effective from their grant date.
Stock-based compensation expense				$ 334,000	$ 272,000
Stock options outstanding				129,776
Incentive Awards [Member] | First Tranche [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive awards vested percentage						100.00%

Stock Plan and Stock-Based Co49

Stock Plan and Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares Subject to Outstanding Options
Outstanding at the beginning of period	2,394,388	1,804,083
Options granted	2,224,801	646,667
Options exercised	(472,169)
Options forfeited	(82,578)	(14,319)
Options expired	(9,001)	(42,043)
Outstanding as end of period	4,055,441	2,394,388
Vested and expected to vest	4,055,441
Exercisable	1,973,842
Weighted-Average Exercise Price of Options
Outstanding at the beginning of period	$ 5.46	$ 7.41
Options granted	4.79	1.28
Options exercised	3.40	0
Options forfeited	1.91	4.50
Options expired	10	25.01
Outstanding as end of period	5.40	$ 5.46
Vested and expected to vest	5.40
Exercisable	$ 5.69
Weighted-Average Remaining Contractual Term (Years)
Outstanding	7 years 3 months 10 days
Vested and expected to vest	7 years 3 months 10 days
Exercisable	5 years 4 months 6 days
Aggregate Intrinsic Value (In Thousands)
Outstanding	$ 15,975
Vested and expected to vest	15,975
Exercisable	$ 7,371
Performance Option [Member]
Shares Subject to Outstanding Options
Outstanding at the beginning of period	327,000
Options granted		327,000
Options exercised	(26,000)
Outstanding as end of period	301,000	327,000
Weighted-Average Exercise Price of Options
Outstanding at the beginning of period	$ 1.82
Options granted		$ 1.82
Options exercised	1.82
Outstanding as end of period	$ 1.82	$ 1.82
Weighted-Average Remaining Contractual Term (Years)
Outstanding	5 years 11 months 1 day
Aggregate Intrinsic Value (In Thousands)
Outstanding	$ 2,200

Stock Plan and Stock-Based Co50

Stock Plan and Stock-Based Compensation - Summary of Stock-Based Compensation Expense, Net of Estimated Forfeitures (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,920	$ 2,473
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,301	995
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,619	$ 1,478

Stock Plan and Stock-Based Co51

Stock Plan and Stock-Based Compensation - Estimated Weighted-Average Grant Date Fair Value (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 years	6 years 1 month 6 days
Expected volatility	84.00%	80.00%
Risk-free interest rate	2.15%	1.57%
Expected dividend yield		0.00%
Weighted-average grant date fair value per share	$ 3.36	$ 0.89
Performance Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term		5 years 1 month 6 days
Expected volatility		85.00%
Risk-free interest rate		1.56%
Expected dividend yield		0.00%
Weighted-average grant date fair value per share		$ 1.20

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Provision for income taxes		$ 0	$ 0
US federal corporate tax rate		35.00%
Limitation of the deduction for net operating losses		80.00%
Net valuation allowance increase (decrease)		$ (32,700,000)
Cumulative change in ownership		50.00%
Cumulative change in ownership period		3 years
Significant change to its unrecognized tax benefits over the next twelve months		$ 0
Income tax examination years		all years remain open for income tax examination by tax authorities
Domestic Tax Authority [Member]
Income Tax [Line Items]
Net operating loss carryforward		$ 255,700,000
Research and development tax credit carry forwards		7,700,000
Domestic Tax Authority [Member] | Orphan Drug [Member]
Income Tax [Line Items]
Research and development tax credit carry forwards		$ 6,000,000
Domestic Tax Authority [Member] | Minimum [Member]
Income Tax [Line Items]
NOL carry forward expiry date		2,024
Domestic Tax Authority [Member] | Maximum [Member]
Income Tax [Line Items]
NOL carry forward expiry date		2,037
State and Local Jurisdiction [Member]
Income Tax [Line Items]
Net operating loss carryforward		$ 146,600,000
Research and development tax credit carry forwards		$ 4,000,000
State and Local Jurisdiction [Member] | Minimum [Member]
Income Tax [Line Items]
NOL carry forward expiry date		2,028
State and Local Jurisdiction [Member] | Maximum [Member]
Income Tax [Line Items]
NOL carry forward expiry date		2,037
Scenario Forecast [Member]
Income Tax [Line Items]
US federal corporate tax rate	21.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 63,935	$ 88,111
Capitalized research and development	9,455	22,272
Federal and state tax credit carryforwards	13,529	8,141
Stock based compensation	1,493	2,080
Other	438	974
Total deferred tax assets	88,850	121,578
Valuation allowance	(88,850)	(121,578)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Expected Statutory Federal Income Tax Provision to Actual Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax benefit at federal statutory tax rate of 34%	$ (9,369)	$ (9,068)
Change in valuation allowance	(32,709)	9,775
Effect of change in enacted tax rates	38,194
State income taxes, net of federal benefit	5,094	(458)
Permanent items	4,027	196
Research credits	(5,237)	(445)
Income tax (benefit) expense	$ 0	$ 0

Income Taxes - Summary of Gross

Income Taxes - Summary of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 2,286	$ 2,127
Increases related to prior year tax positions	0	0
Increases related to tax positions	1,009	159
Balance at end of period	$ 3,295	$ 2,286

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Former Member of Board of Directors [Member]
Related Party Transaction [Line Items]
Advisory fee paid to related party	$ 60,000	$ 60,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Feb. 01, 2018	Jul. 24, 2017	Feb. 07, 2017	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Common stock, shares issued		14,950,000	5,181,348		44,408,796	23,447,003
Common stock offering price		$ 6.50	$ 1.93
Net proceeds from public offering		$ 91.1	$ 9.2
Subsequent Event [Member]
Subsequent Event [Line Items]
Common stock, shares issued	13,340,000
Common stock offering price	$ 10.80
Net proceeds from public offering	$ 135.5			$ 135.5