Ardelyx (ARDX) 10-K 4 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Mar. 02, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Trading Symbol	ARDX
Entity Registrant Name	Ardelyx, Inc.
Entity Central Index Key	1,437,402
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		34,628,898
Entity Public Float			$ 230,851,093

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 107,004	$ 107,286
Accounts receivable		2,584
Prepaid expenses and other current assets	5,027	1,209
Total current assets	112,031	111,079
Property and equipment, net	4,711	2,131
Other assets	104	104
Restricted cash	100	100
Total assets	116,946	113,414
Current liabilities:
Accounts payable	2,777	3,129
Accrued compensation and benefits	2,366	1,648
Accrued and other liabilities	2,580	780
Deferred revenue, current portion		15,979
Total current liabilities	7,723	21,536
Other long-term liabilities	322	122
Deferred revenue, non-current		31,074
Total liabilities	$ 8,045	$ 52,732
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized as of December 31, 2015 and December 31, 2014, respectively; no shares issued and outstanding as of December 31, 2015 and December 31, 2014, respectively.
Common stock, $0.0001 par value; 300,000,000 shares authorized as of December 31, 2015 and December 31, 2014, respectively; 25,964,886 and 18,589,245 shares issued and outstanding as of December 31, 2015 and December 31, 2014, respectively.	$ 3	$ 2
Additional paid-in capital	210,386	132,547
Accumulated deficit	(101,488)	(71,867)
Total stockholders' equity	108,901	60,682
Total liabilities and stockholders' equity	$ 116,946	$ 113,414

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	25,964,886	18,589,245
Common stock, shares outstanding	25,964,886	18,589,245

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue:
Licensing revenue	$ 21,611	$ 18,394	$ 8,063
Collaborative development revenue	2,415	13,229	20,865
Total revenue	24,026	31,623	28,928
Operating expenses:
Research and development	39,885	25,900	28,093
General and administrative	13,530	7,287	3,700
Total operating expenses	53,415	33,187	31,793
Loss from operations	(29,389)	(1,564)	(2,865)
Other income (expense), net	(261)	10	(52)
Change in fair value of preferred stock warrant liability		(1,593)	(3,506)
Loss before provision for income taxes	(29,650)	(3,147)	(6,423)
Benefit from (provision for) income taxes	29	(67)	(141)
Net loss and comprehensive loss	$ (29,621)	$ (3,214)	$ (6,564)
Net loss per common share, basic and diluted	$ (1.29)	$ (0.31)	$ (5.82)
Shares used to compute net loss per common share, basic and diluted	22,892,640	10,248,337	1,127,948

Statements of Convertible Prefe

Statements of Convertible Preferred Stock and Stockholders Equity (Deficit) - USD ($) $ in Thousands	Total	IPO [Member]	Private Placement [Member]	Convertible Preferred Stock [Member]	Convertible Preferred Stock [Member]Private Placement [Member]	Common Stock [Member]	Common Stock [Member]IPO [Member]	Common Stock [Member]Private Placement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]IPO [Member]	Additional Paid-in Capital [Member]Private Placement [Member]	Accumulated Deficit [Member]
Balance, amount at Dec. 31, 2012	$ (57,392)			$ 56,155					$ 4,697			$ (62,089)
Balance, shares at Dec. 31, 2012				11,517,222		1,001,616
Exercise of stock options and vesting of early exercised stock options, net of repurchases, amount	$ 125								125
Exercise of stock options and vesting of early exercised stock options, net of repurchases, shares	223,865					223,865
Stock-based compensation	$ 352								352
Net loss	(6,564)											(6,564)
Balance, amount at Dec. 31, 2013	(63,479)			$ 56,155					5,174			(68,653)
Balance, shares at Dec. 31, 2013				11,517,222		1,225,481
Conversion of convertible preferred stock to common stock in connection with initial public offering, amount	56,155			$ (56,155)		$ 1			56,154
Conversion of convertible preferred stock to common stock in connection with initial public offering, shares				(11,517,222)		11,517,222
Net exercise and conversion of preferred stock warrants to common stock in connection with initial public offering, amount	8,049								8,049
Net exercise and conversion of preferred stock warrants to common stock in connection with initial public offering, shares						571,244
Exercise of stock options and vesting of early exercised stock options, net of repurchases, amount	$ 238								238
Exercise of stock options and vesting of early exercised stock options, net of repurchases, shares	336,398					336,398
Issuance of common stock for services, amount	$ 208								208
Issuance of common stock for services, shares	10,000					10,000
Issuance of common stock and warrants in connection with the private placement, net of expenses		$ 61,241					$ 1			$ 61,240
Issuance of common stock and warrants in connection with the private placement, shares							4,928,900
Stock-based compensation	$ 1,484								1,484
Net loss	(3,214)											(3,214)
Balance, amount at Dec. 31, 2014	60,682					$ 2			132,547			(71,867)
Balance, shares at Dec. 31, 2014						18,589,245
Exercise of stock options and vesting of early exercised stock options, net of repurchases, amount	$ 111								111
Exercise of stock options and vesting of early exercised stock options, net of repurchases, shares	77,784					77,784
Issuance of common stock for services, amount	$ 194								194
Issuance of common stock under employee stock purchase plan ,amount	$ 548					$ 0			548
Issuance of common stock for services, shares	13,285					13,285
Issuance of common stock under employee stock purchase plan , shares						41,580
Issuance of common stock and warrants in connection with the private placement, net of expenses			$ 74,323		$ 0			$ 1			$ 74,322
Issuance of common stock and warrants in connection with the private placement, shares								7,242,992
Stock-based compensation	$ 2,634								2,634
Other	30								30
Net loss	(29,621)											(29,621)
Balance, amount at Dec. 31, 2015	$ 108,901					$ 3			$ 210,386			$ (101,488)
Balance, shares at Dec. 31, 2015						25,964,886

Statements of Convertible Pref6

Statements of Convertible Preferred Stock and Stockholders Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Private Placement [Member]
Stock issuance costs	$ 3,449

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (29,621)	$ (3,214)	$ (6,564)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	829	302	592
Amortization of deferred financing costs	351
Amortization of deferred compensation for services	107
Stock-based compensation	2,634	1,692	352
Change in fair value of preferred stock warrant liability		1,593	3,506
Loss from disposal of fixed assets	65
Changes in operating assets and liabilities:
Accounts receivable	2,584	3,852	(3,364)
Prepaid expenses and other assets	(4,083)	96	(438)
Accounts payable	(371)	831	1,138
Accrued compensation and benefits	718	721	(38)
Accrued and other liabilities	2,000	647	(1,009)
Deferred revenue	(47,053)	6,755	7,636
Other long-term liabilities		122
Net cash (used in) provided by operating activities	(71,840)	13,397	1,811
Investing activities
Purchases of property and equipment	(3,454)	(1,856)	(278)
Net cash used in investing activities	(3,454)	(1,856)	(278)
Financing activities
Proceeds from issuance of common stock, net	74,323	61,241
Proceeds from issuance of common stock from exercise of options	659	71	1
Other	30	(2)	(2)
Net cash provided by (used in) financing activities	75,012	61,310	(1)
Net increase in cash and cash equivalents	(282)	72,851	1,532
Cash and cash equivalents at beginning of period	107,286	34,435	32,903
Cash and cash equivalents at end of period	107,004	107,286	34,435
Supplementary disclosure of cash flow information
Income taxes paid	69		160
Supplementary disclosure of non-cash financing information:
Acquisition of property and equipment included in accounts payable and accrued liabilities	$ 0	0	$ 0
Services settled through the issuance of common stock		208
Reclassification of convertible preferred warrant liability to additional paid-in capital		8,049
Conversion of convertible preferred stock to common stock at closing of initial public offering		$ 56,155

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. ORGANIZATION AND BASIS OF PRESENTATION Ardelyx, Inc. (the “Company”) is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of innovative, minimally-systemic therapeutic drugs that work exclusively in the gastrointestinal, or GI, tract to treat GI and cardio-renal. The Company has developed a proprietary drug discovery and design platform enabling it, in a rapid and cost-efficient manner, to discover and design novel drug candidates. Utilizing its platform, the Company discovered and designed its lead product candidate, tenapanor, which is currently being evaluated in two pivotal Phase 3 clinical studies in patients with constipation-predominant irritable bowel syndrome, or IBS-C. In a Phase 2b clinical study, tenapanor demonstrated the ability to lower elevated serum phosphorus levels in patients with end-stage renal disease, or ESRD. The Company has initiated an additional Phase 2b clinical trial to evaluate dosing regimens of tenapanor for the treatment of hyperphosphatemia, or elevated serum phosphorus in ESRD patients. The Company is developing another drug candidate, RDX022, for the treatment of hyperkalemia, or elevated serum potassium. The Company is pursuing a 505(b)(2) regulatory pathway for RDX022. The Company has additional drug candidates in earlier stages of research and development focused in GI and cardio-renal diseases including RDX009, a secretagogue of glucagon-like peptide-1, or GLP-1, and glucagon-like peptide-2, or GLP-2, and RDX013, a potassium secretagogue. The Company was incorporated in Delaware on October 17, 2007, under the name Nteryx and changed its name to Ardelyx, Inc. in June 2008. The Company operates in only one business segment, which is the development of biopharmaceutical products. Initial Public Offering On June 18, 2014, the Company’s registration statement on Form S-1 (File No. 333-196090) relating to the initial public offering (the “IPO”) of its common stock was declared effective by the SEC, and the IPO closed on June 24, 2014. The Company sold 4,928,900 shares of its common stock, which included the exercise in full by the underwriters of the IPO of their option to purchase 642,900 additional shares of the Company’s common stock, and the Company received cash proceeds of $61.2 million from the IPO, net of $7.8 million underwriting discounts and commissions and expenses paid by the Company. On June 24, 2014, prior to the closing of the IPO, all outstanding shares of convertible preferred stock converted into 11,517,222 shares of common stock with the related carrying value of $56.2 million being reclassified to common stock and additional paid-in capital. In addition, all convertible preferred stock warrants were net exercised and the related convertible preferred stock warrant liability was reclassified to additional paid-in capital. On June 24, 2014, the Company’s Amended and Restated Certificate of Incorporation became effective and the number of shares of capital stock the Company is authorized to issue was increased to 305,000,000 shares, of which 300,000,000 shares may be common stock and 5,000,000 shares may be preferred stock. Both the common stock and preferred stock have a par value of $0.0001 per share. There are no shares of preferred stock outstanding at December 31, 2015 or 2014.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The Company’s financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”). Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, clinical trial accruals, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity date of 90 days or less on the date of purchase to be cash equivalents. The Company invests its cash in bank deposits and money market funds. Cash overdrafts An overdraft totaling $1.5 million was classified as accounts payable at December 31, 2015. The Company’s policy is to report the change in overdrafts as an operating activity in the Statements of Cash Flows. Restricted Cash The Company is required to guarantee the credit limit on its corporate credit card with a certificate of deposit of $0.1 million. The collateral will be released upon the cancellation of the corporate credit card. Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. Cash and cash equivalents are invested through banks and other financial institutions in the United States. Such deposits may be in excess of insured limits. The Company maintains cash and cash equivalents and investments with various high credit quality and capitalized financial institutions. Property and Equipment Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the lesser of the estimated useful lives or the related remaining lease term. Impairment of Long-Lived Assets The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2015, there have been no such impairment losses. Income Taxes The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Revenue Recognition Revenue from research activities made under collaboration partnership agreements are recognized as the services are provided and when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collectability is reasonably assured. Revenue generated from research and licensing agreements typically includes up-front signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments, and royalties on future licensees’ product sales. For revenue agreements with multiple-element arrangements, such as license and development agreements, the Company allocates revenue to each unit of accounting based on the relative selling price of each unit. When applying the relative selling price method, the Company determines the selling price for each deliverable using vendor-specific objective evidence or third-party evidence. If neither exists, the Company uses its best estimate of selling price for that deliverable. Revenue allocated is then recognized when the four basic revenue recognition criteria are met for each deliverable. The Company recognizes revenue from upfront payments ratably over the term of its estimated period of performance under the agreement which is recorded as licensing revenue. Reimbursements for development costs incurred under the Company’s license agreement with AstraZeneca are classified as collaborative development revenue. The Company recognizes cost reimbursement revenue under collaboration partnership agreements as the related research and development costs for services are rendered. Deferred revenue represents the portion of research or license payments received which has not been earned. Revenues from milestones, if they are nonrefundable and deemed substantive, are recognized upon successful accomplishment of the milestones. To the extent that non-substantive milestones are achieved and the Company has remaining performance obligations, milestones are deferred and recognized as revenue over the estimated remaining period of performance. The Company will recognize revenue associated with the non-substantive milestones upon achievement of the milestone if there are no undelivered units and it has no remaining performance obligations. The Company will account for sales-based milestones as royalties that will be recognized as revenue upon achievement of the milestone. Stock-Based Compensation The Company measures its stock-based payment awards made to employees and directors based on the estimated fair values of the awards and recognizes the compensation expense over the requisite service period. The Company has selected the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. Stock-based compensation expense is recognized using the straight-line method. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company accounts for compensation expense related to stock options granted to non-employees based on the fair values estimated using the Black-Scholes model. Stock options granted to non-employees are remeasured at each reporting date until the award is vested. Research and Development Costs Research and development expenditures are expensed as incurred. Major components of research and development expenses consist of personnel costs, materials and supplies, and allocations of facilities-related costs, as well as fees paid to consultants and third parties that conduct certain research and development activities on the Company’s behalf. Payments made to other entities are under agreements that are generally cancelable by the Company. Nonrefundable advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. Convertible Preferred Stock Warrant Liability The Company accounted for freestanding warrants to purchase shares of convertible preferred stock that were contingently redeemable as liabilities in the balance sheets at their estimated fair value. Convertible preferred stock warrants were subject to remeasurement at each balance sheet date, and any change in fair value was recognized as a component of other expense, net in the statements of operations and comprehensive loss. The Company continued to adjust the carrying value of the warrants until the closing of the IPO, at which time the warrants were net exercised for shares of the Company’s common stock and the liability was reclassified to stockholders’ equity (deficit). Comprehensive Loss Comprehensive loss is composed of two components: net loss and other comprehensive loss. Other comprehensive income (loss) refers to gains and losses that under GAAP are recorded as an element of stockholders’ equity (deficit), but are excluded from net loss. The Company did not record any transactions within other comprehensive income (loss) in the periods presented and, therefore, the net loss and comprehensive loss were the same for all periods presented. Net Loss per Share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share in the periods presented is the same as basic net loss per common share, since the effects of potentially dilutive securities are antidilutive. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ In November 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) The Company has reviewed all other significant newly-issued accounting pronouncements and concluded that they either are not applicable to the Company’s operations or that no material effect is expected on its financial statements as a result of future adoption.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. FAIR VALUE MEASUREMENTS 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 on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows: Level 1 – Valuations are based on quoted prices in active markets for identical assets or liabilities and readily accessible by us at the reporting date. Examples of assets and liabilities utilizing Level 1 inputs are certain money market funds, U.S. Treasuries and trading securities with quoted prices on active markets. Level 2 – Valuations based on inputs other than the quoted prices in active markets that are observable either directly or indirectly in active markets. Examples of assets and liabilities utilizing Level 2 inputs are U.S. government agency bonds, corporate bonds, commercial paper, certificates of deposit and over-the-counter derivatives. Level 3 – Valuations based on unobservable inputs in which there is little or no market data, which require us to develop our own assumptions. The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy: December 31, 2015 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 105,819 $ 105,819 $ — $ — Certificates of deposit 100 — 100 — Total $ 105,919 $ 105,819 $ 100 $ — December 31, 2014 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 105,410 $ 105,410 $ — $ — Certificates of deposit 100 — 100 — Total $ 105,510 $ 105,410 $ 100 $ — Where quoted prices are available in an active market, securities are classified as Level 1. The Company classifies money market funds as Level 1. When quoted market prices are not available for the specific security, then the Company estimates fair value by using benchmark yields, reported trades, broker/dealer quotes, and issuer spreads. The Company classifies certificates of deposit as Level 2. In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3. There were no transfers between Level 1 and Level 2 during the periods presented. The carrying amounts reflected in the balance sheets for cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values at both December 31, 2015 and December 31, 2014, due to their short-term nature.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property and Equipment	4. PROPERTY AND EQUIPMENT Property and equipment consist of the following: December 31, 2015 2014 (in thousands) Laboratory equipment $ 4,471 $ 3,039 Office equipment and furniture 134 229 Construction in progress — 362 Leasehold improvements 3,914 2,135 Property and equipment, gross 8,519 5,765 Less: accumulated depreciation (3,808 ) (3,634 ) Total property and equipment, net $ 4,711 $ 2,131 Depreciation and amortization expense totaled $0.8 million, $0.3 million and $0.6 million for the years ended December 31, 2015, 2014 and 2013.

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration and Licensing Agreements	5. COLLABORATION AND LICENSING AGREEMENTS AstraZeneca AB (“AstraZeneca”) In October 2012, the Company entered into a collaboration partnership with AstraZeneca for the worldwide development and commercialization of tenapanor. Under the terms of the AstraZeneca collaboration partnership agreement, or the AstraZeneca Agreement, the Company received an up-front license fee of $35.0 million in October 2012, a $15.0 million payment in December 2013 and a $25.0 million payment in May 2014. The amounts were recorded as deferred revenue when received and were recognized as revenue on a straight-line basis over the remaining estimated period of performance under the AstraZeneca Agreement, which during the three months ended March 31, 2015, the Company estimated to extend to December 2017. In June 2015, the Company entered into a termination agreement with AstraZeneca (the “Termination Agreement”) pursuant to which all licenses granted to AstraZeneca to the Company’s portfolio of NHE3 inhibitors, including the Company’s lead product candidate, tenapanor, were terminated, except for the limited purpose of allowing AstraZeneca to satisfy its obligations under the Termination Agreement. Under the terms of the Termination Agreement, the Company agreed to pay AstraZeneca certain amounts for the return of the licenses granted to it, including (a) an upfront fee of $15.0 million, (b) future royalties at a royalty rate of 10% of net sales of tenapanor or other NHE3 products by the Company or its licensees, and (c) 20% of non-royalty revenue received from a new collaboration partner should the Company elect to license, or otherwise provide rights to develop and commercialize tenapanor, or another NHE3 inhibitor. The amounts payable by the Company as described in (a)-(c) are capped at the aggregate amount of $90.0 million. The Company also paid AstraZeneca $10.0 million as reimbursement for certain research and development expenses incurred by AstraZeneca under the collaboration agreement during 2015 and in consideration of the acceleration of the transfer of information and materials to the Company. In addition, AstraZeneca was obligated to supply the Company with clinical trial materials, drug substance and drug product. The maximum amount that the Company was obligated to pay for such materials was set at $10 million in the Termination Agreement, which maximum amount was subsequently reduced to $8.0 million pursuant to an amendment to the Termination Agreement (“Amendment Number One”). As the AstraZeneca Agreement was terminated in June 2015, the Company recognized the remaining deferred revenue balance of $43.1 million during the three months ended June 30, 2015. Also in the three months ended June 30, 2015, the Company recorded the $15.0 million upfront payment for the return of the licenses as well as the $10.0 million payment for reimbursement of research and development expenses and the acceleration of the transfer of information and materials as a reduction in licensing revenue. The Company recorded $7.3 million in expenses incurred for the tenapanor clinical trial material from AstraZeneca during the year ended December 31, 2015. Sanofi SA (“Sanofi”) In February 2014, the Company entered into a license option and license agreement with Sanofi (the“Sanofi Agreement”) for its phosphate transport NaP2b inhibitor program. Under the terms of the Sanofi Agreement, the Company granted Sanofi an exclusive worldwide license to conduct research utilizing the Company’s small molecule NaP2b inhibitors. In addition, Sanofi had the option to obtain an exclusive license to develop, manufacture and commercialize potential products under the agreement. Under the Sanofi Agreement, the Company received a payment of $1.25 million in March 2014, which was fully recognized as licensing revenue in May 2014 after the Company completed its obligation to provide to Sanofi the background know-how, listed patents, and materials described in the Sanofi Agreement. The Sanofi Agreement was terminated effective September 30, 2015 and all rights were returned to the Company. There was no payment associated with termination and the return of rights to the Company.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2015
Text Block [Abstract]
Convertible Preferred Stock	6. CONVERTIBLE PREFERRED STOCK On June 24, 2014, prior to the closing of the IPO, all outstanding shares of convertible preferred stock converted into 11,517,222 shares of common stock with the related carrying value of $56.2 million reclassified to common stock and additional paid-in capital.

Preferred Stock Warrants

Preferred Stock Warrants	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Preferred Stock Warrants	7. PREFERRED STOCK WARRANTS In connection with the closing of the Series B financing in August 2011, the Company issued warrants for the purchase of 574,953 shares of Series B convertible preferred stock. The exercise price of the warrants was $0.09 per share. The preferred stock warrant liability was measured at fair value on a recurring basis. Changes in fair value were recorded in change in fair value of preferred stock warrant liability in the Statements of Operations and Comprehensive Loss. As of December 31, 2013 and for the period in 2014 up to the IPO date, the Company revalued the warrants using a hybrid of the option pricing method and the probability-weighted expected return method. The hybrid methodology was applied to reflect two exit scenarios, IPO and merger using a market approach and the income approach was used in the stay private scenario. The scenarios were weighted based on the Company’s estimate of the probability of each scenario: 20% for IPO; 10% for merger and 70% for stay private for the year ended December 31, 2013. As of December 31, 2013, the fair value of this convertible preferred stock warrant liability amounted to $6.5 million. Just prior to the IPO close date of June 24, 2014, the preferred stock warrant liability was remeasured prior to the net exercise of the warrants using the IPO price.

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Incentive Plans	8. EQUITY INCENTIVE PLANS 2008 Plan The Company granted options under its 2008 Stock Incentive Plan (the “2008 Plan”) until June 2014 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2008 Plan. The 2008 Plan provided for the granting of incentive and nonstatutory stock options, and stock purchase rights to employees, directors and consultants at the discretion of the Board of Directors. Stock options granted generally vest over a period of four years from the date of grant. In connection with the Board of Directors and stockholders approval of the 2014 Plan, all remaining shares available for future award under the 2008 Plan were transferred to 2014 Plan, and the 2008 Plan was terminated. 2014 Plan The 2014 Equity Incentive Award Plan (“2014 Plan”) became effective on June 18, 2014, immediately prior to the time the Company’s Registration Statement on Form S-1 became effective. Under the 2014 Plan, 1,419,328 shares of common stock were initially reserved for issuance pursuant to a variety of stock-based compensation awards, including stock options, stock appreciation rights, or SARs, restricted stock awards, restricted stock unit awards, deferred stock awards, deferred stock unit awards, dividend equivalent awards, stock payment awards and performance awards. In addition, 35,221 shares that had been available for future awards under the 2008 Plan as of June 18, 2014, were added to the initial reserve available under the 2014 Plan, bringing the total reserve upon the effective date of the 2014 Plan to 1,454,549. The number of shares initially reserved for issuance or transfer pursuant to awards under the 2014 Plan will be increased by (i) the number of shares represented by awards outstanding under 2008 Plan on June 18, 2014, that are either forfeited or lapse unexercised or that are repurchased for the original purchase price thereof, up to a maximum of 1,153,279 shares, and (ii) if approved by the Administrator of the 2014 Plan, an annual increase on the first day of each fiscal year ending in 2024, equal to the lesser of (A) four percent (4.0%) of the shares of stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (B) such smaller number of shares of stock as determined by our board of directors; provided, however, that no more than 10,683,053 shares of stock may be issued upon the exercise of incentive stock options. Effective January 1, 2016, the 2014 Plan share reserve was increased by 1,038, 595 shares. Stock Plan Activity The following table summarizes activity under the 2008 Plan and the 2014 Plan, including grants to nonemployees and restricted stock issued: Options Issued and Outstanding Shares Available for Number of Shares Average Exercise Aggregate (in thousands) Balance at December 31, 2012 96,841 1,293,767 $ 0.77 Options granted (99,552 ) 99,552 3.42 Options exercised — (223,865 ) 0.56 Options canceled 6,625 (6,625 ) 2.23 Balance at December 31, 2013 3,914 1,162,829 $ 1.03 Options authorized 1,452,661 — Options granted (188,888 ) 188,888 24.41 Options exercised — (336,398 ) 0.71 Options canceled 4,084 (4,084 ) 2.21 Options repurchased 3,511 (3,511 ) 0.55 Issuance of common stock for services (10,000 ) — — Balance at December 31, 2014 1,265,282 1,007,724 $ 5.51 Options authorized 743,569 — Options granted (379,709 ) 379,709 19.60 Options exercised — (77,784 ) 1.42 Options canceled 28,563 (28,563 ) 12.41 Issuance of common stock for services (13,285 ) — — Balance at December 31, 2015 1,644,420 1,281,086 $ 9.78 $ 13,129 Vested and expected to vest at December 31, 2015 1,259,972 $ 9.59 $ 13,096 Vested at December 31, 2015 835,860 $ 4.36 $ 12,075 The weighted-average grant-date estimated fair value of options granted during the years ended December 31, 2015, 2014 and 2013 was $12.91, $18.53 and $2.68 per share. The aggregate intrinsic value was calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock of $18.12 per share as of December 31, 2015. The total fair value of options that vested during the years ended December 31, 2015, 2014 and 2013 was $2.4 million, $0.5 million and $0.2 million, respectively. Employee Stock Purchase Plan The Company adopted the 2014 Employee Stock Purchase Plan (ESPP) and initially reserved 202,762 shares of common stock as of its effective date of June 18, 2014. If approved by the Administrator of the ESPP, on the first day of each calendar year, ending in 2024, the number of shares in the reserve will increase by an amount equal to the lesser of (i) one percent (1.0%) of the shares of common stock outstanding on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the board of directors; provided, however, no more than 2,230,374 shares of our common stock may be issued under the ESPP. Effective January 1, 2015, the ESPP share reserve was increased by 185,892. Under the ESPP, participants are offered the option to purchase shares of the Company’s common stock at a discount during a series of successive offering periods normally commencing on March 1 and September 1 of each year. The initial offering period commenced on September 1, 2014 and will end on February 27, 2015. The number of shares authorized for issuance under the ESPP as of December 31, 2015 was 388,654, of which 347,074 shares were available for future issuance. The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of ESPP purchase rights granted to employees: Year Ended December 31, 2015 2015 2014 Expected term ( years) 0.5 0.5 Volatility 97 % 73 % Risk-free interest rate 0.16 % 0.05 % Dividend yield — % — % There were no shares issued during the year ended December 31, 2014 under the ESPP. In 2015, the Company sold 41,580 shares of its common stock under the ESPP. The shares were purchased at a weighted-average purchase price of $13.25 with proceeds of approximately $0.6 million. Modification of Stock Awards During September 2014, the Company entered into a Transition and Separation Agreement with its Chief Scientific Officer, Dominique Charmot, under which certain restricted shares that were subject to vesting and repurchase by the Company have become fully vested as of Dr. Charmot’s separation from the Company as an employee and director on December 23, 2014. This resulted in the acceleration of the vesting for 58,969 shares of restricted stock. As a result of the acceleration, the Company has recorded a stock-based compensation charge of $0.8 million during the year ended December 31, 2014 to reflect the revised service period for the restricted stock and related vesting of shares that would otherwise not have vested. Offering of Common Stock and Warrants In June 2015, the Company sold and issued an aggregate of 7,242,992 shares of its common stock and warrants to purchase 2,172,899 shares of common stock for aggregate gross proceeds of approximately $77.8 million or net proceeds, after deducting issuance costs, of approximately $74.3 million. The purchase price for the common stock was $10.70 per share and the purchase price for the warrants was $0.125 per warrant. The warrants are exercisable for an exercise price of $13.91 per share at any time prior to the earlier of (i) 5 years from the date of issuance or (ii) certain changes in control of the Company. The Company has determined that the warrants should be classified as equity. In July 2015, the Company filed a registration statement with the SEC with respect to the common stock and warrants. Other than with respect to warrants issued to holders affiliated with New Enterprise Associates, the warrants contain limitations that prevent each holder of warrants from acquiring shares upon exercise of the warrants that would cause the number of shares beneficially owned by it and its affiliates to exceed 9.99% of the total number of shares of the Company’s common stock then issued and outstanding. In addition, upon certain changes in control of the Company, each holder of a warrant can elect to receive, subject to certain limitations and assumptions, securities in a successor entity. None of the warrants issued in June 2015 have been exercised during the year ended December 31, 2015. Stock-based Compensation Total stock-based compensation recognized was as follows (in thousands): Year Ended December 31, 2015 2014 2013 (in thousands) Research and development $ 1,327 $ 1,376 $ 200 General and administrative 1,307 316 152 Total stock-based compensation $ 2,634 $ 1,692 $ 352 As of December 31, 2015, the Company had $5.6 million and $0.1 million of total unrecognized compensation expense, net of estimated forfeitures, related to stock option grants and purchase rights, respectively, that will be recognized over an average vesting period of 2.6 years and 0.2 years, respectively. The estimated grant date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following weighted assumptions: Year Ended December 31, 2015 2014 2013 Expected term (years) 5.89 5.97 6.07 Volatility 75 % 94 % 98 % Risk-free interest rate 1.64 % 1.79 % 1.35 % Dividend yield — % — % — % Expected Term Expected Volatility Risk-Free Interest Rate Expected Dividend Options Granted to Nonemployees The Company has granted options to purchase shares of common stock to consultants in exchange for services performed. The Company granted options to purchase 5,000, 10,000 and 3,333 shares with average exercise prices of $18.58, $20.77 and $3.43 per share, respectively, during the years ended December 31, 2015, 2014 and 2013, respectively. These options vest upon grant or various terms up to three years. The Company recognized non-employees stock compensation expense of $0.2 million, $0.1 million and insignificant during the years ended December 31, 2015, 2014 and 2013, respectively. The fair value of non-employees’ options was measured using the Black-Scholes option-pricing model reflecting the same assumptions as applied to employee options in each of the reported years, other than the expected life, which is assumed to be the remaining contractual life of the option. Issuance of Common Stock for Services During the year ended December 31, 2015, the Company issued 13,285 shares of common stock in exchange for services performed. The shares issued were valued at $0.2 million based on the fair value of the common stock on the date of grant. During the year ended December 31, 2014, the Company issued 10,000 shares of common stock in exchange for services performed. The shares issued were valued at $0.2 million based on the fair value of the common stock on the date of grant.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	9. INCOME TAXES The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate: December 31, 2015 2014 2013 Expected income tax provision at the federal statutory rate 35.0 % 35.0 % 35.0 % State taxes, net of federal benefit (3.8 ) 4.6 (1.4 ) Change in valuation allowance (30.7 ) (17.9 ) (22.6 ) Nondeductible expenses — (20.6 ) (20.8 ) Tax credits 1.3 — 7.3 Other (1.7 ) (3.2 ) 0.3 Income tax provision 0.1 % (2.1 %) (2.2 %) Significant components of the Company’s deferred tax assets are as follows: December 31, 2015 2014 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 30,572 $ 11,262 Deferred revenue — 11,099 Research credits 1,919 1,260 Other 1,582 1,201 Gross deferred tax assets 34,073 24,822 Valuation allowance (33,845 ) (24,741 ) Total deferred tax assets 228 81 Deferred tax liabilities (228 ) (81 ) Net deferred tax assets $ — $ — Realization of deferred tax assets is dependent on future earnings, if any, the timing and amount of which are uncertain. Accordingly, the deferred tax assets have been fully offset by a valuation allowance. The valuation allowance increased by approximately $9.1 million for the year ended December 31, 2015. The valuation allowance decreased by approximately $0.3 million for the year ended December 31, 2014. At December 31, 2015, the Company had net operating loss carryforwards for federal income tax purposes of approximately $85.2 million that expire beginning in 2030 if not utilized, and federal research and development tax credit carryforwards of approximately $2.7 million that expire beginning in 2027 if not utilized. In addition, the Company had net operating loss carryforwards for California income tax purposes of approximately $32.3 million that expire beginning in 2030 if not utilized, and state research and development tax credit carryforwards of approximately $3.0 million which can be carried forward indefinitely. Finally, the Company had approximately insignificant and $0.2 million of minimum tax credit carryovers for federal and California income tax purposes, respectively. The minimum tax credits have no expiration date. As a result of certain realization requirements of ASC 718, the table of deferred tax assets and liabilities does not include certain deferred tax assets as of December 31, 2015, and December 31, 2014, that arose directly from tax deductions related to equity compensation that are greater than the compensation recognized for financial reporting. Equity will be increased by approximately $0.7 million if and when such deferred tax assets are ultimately realized. We use ASC 740 ordering when determining when excess tax benefits have been realized. The future utilization of the net operating loss and tax credit carryforwards and credits may be subject to an annual limitation, pursuant to Internal Revenue Code Sections 382 and 383, as a result of ownership changes that may have occurred previously or that could occur in the future. Due to the existence of the valuation allowance, future changes under Sections 382 and 383 will not impact the Company’s effective tax rate. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2015 2014 2013 (in thousands) Balance at beginning of year $ 2,815 $ 1,411 $ 1,064 Additions (subtractions) based on tax positions related to prior year (58 ) 405 — Additions based on tax positions related to current year 541 999 347 Balance at end of year $ 3,298 $ 2,815 $ 1,411 The unrecognized tax benefits, if recognized and in absence of full valuation allowance, would impact the income tax provision by $3.3 million, $2.8 million and $1.4 million as of December 31, 2015, 2014 and 2013, respectively. The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2015, 2014 and 2013, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. Although the timing and outcome of income tax audit is highly uncertain, the Company does not anticipate that the amount of existing unrecognized tax benefits will significantly change during the next 12 months. The Company files income tax returns in the U.S. federal, California and Massachusetts tax jurisdictions. Due to the Company’s net operating loss and tax credit carryforwards, the income tax returns remain open to U.S. federal and California state tax examinations. The Company is not currently under examination in any tax jurisdiction.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Net Loss per Share	10. NET LOSS PER SHARE Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, less shares subject to repurchase, and excludes any dilutive effects of share-based awards and warrants. Diluted net loss per common share is computed giving effect to all potential dilutive common shares, including common stock issuable upon exercise of stock options, and unvested restricted common stock and stock units. As the Company had net losses for the years ended December 31, 2015, 2014 and 2013, all potential common shares were determined to be anti-dilutive. The following table sets forth the computation of net loss per common share (in thousands, except share and per share amounts): December 31, 2015 2014 2013 Numerator: Net loss $ (29,621 ) $ (3,214 ) $ (6,564 ) Denominator: Weighted average number of shares outstanding—basic and diluted 22,892,640 10,248,337 1,127,948 Net loss per share—basic and diluted $ (1.29 ) $ (0.31 ) $ (5.82 ) Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: December 31, 2015 2014 2013 Convertible preferred stock — — 11,517,222 Options to purchase common stock 1,244,442 1,007,724 1,162,829 Warrants to purchase convertible preferred stock — — 574,953 Warrants to purchase common stock 300,302 — — Total 1,544,744 1,007,724 13,255,004

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2015
Clinical Operations Consulting Arrangement [Member] | Spouse of Executive Officer [Member]
Related Party Transactions	11. RELATED PARTY TRANSACTIONS There were no related party transactions in 2015. As part of the consulting arrangement with the spouse of an executive of the Company to provide research and development services related to clinical operations, the Company incurred expenses of $0.2 million for services rendered during each of the years ended December 31, 2014 and 2013, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. COMMITMENTS AND CONTINGENCIES The Company has a lease agreement for a facility in Fremont, California that was amended in December 2012 to extend the lease agreement to September 2016. In September 2014, the Company signed the second amendment to its facility lease agreement in Fremont, California to add space and to extend the lease term through September 2019. In addition, the amended lease agreement provides for a tenant improvement allowance of up to $0.6 million. The extended lease has rent escalation clauses through the lease term. Rent increases, including the impact of a rent holiday and leasehold improvement allowance from the landlord, will be recognized as deferred rent and amortized on a straight-line basis over the term of the lease. Under the terms of the lease agreement, the Company provided the lessor with a security deposit in the amount of $0.1 million. The lessor shall be entitled to draw on the security deposit in the event of any uncured default by the Company under the terms of the lease. The future minimum payments under the noncancelable operating lease at December 31, 2015, are as follows (in thousands): Year ending December 31, Amounts 2016 868 2017 895 2018 921 2019 653 Total $ 3,337 Rent expense under operating leases was $0.9 million, $0.6 million and $0.5 million for the years ended December 31, 2015, 2014 and 2013, respectively. The Company entered into a series of purchase commitments at December 31, 2015 totaling $2.3 million, all of which will be due within the next year. Guarantees and Indemnifications The Company indemnifies each of our officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at our request in such capacity, as permitted under Delaware law and in accordance with our certificate of incorporation and bylaws. The term of the indemnification period lasts as long as an officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance allows the transfer of risk associated with our exposure and may enable the Company to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, the Company has not recognized any liabilities relating to these obligations for any period presented.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	13. SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) Selected quarterly financial results from operations for the years ended December 31, 2015 and 2014 are as follows (in thousands, except per share amounts): 2015 Quarter End March 31, June 30 September 30 December 31 Total revenue $ 5,883 $ 18,143 $ — $ — Operating expenses 9,373 9,087 18,079 16,876 Net (loss) income (3,502 ) 9,007 (18,126 ) (17,000 ) Net (loss) income per share: Basic (0.19 ) 0.43 (0.70 ) (0.65 ) Diluted (0.19 ) 0.42 (0.70 ) (0.65 ) 2014 Quarter End March 31, June 30 September 30 December 31 Total revenue $ 8,550 $ 9,137 $ 7,598 $ 6,338 Operating expenses 9,014 6,386 7,517 10,270 Net (loss) income (3,071 ) 3,753 74 (3,970 ) Net (loss) income per share: Basic (2.44 ) 0.20 — (0.21 ) Diluted (2.44 ) 0.18 — (0.21 )

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	14. SUBSEQUENT EVENTS In January 2016, the Company completed the sale and issuance of an aggregate of 8,625,000 shares of Common Stock. The Company received net proceeds from the Offering of approximately $80.4 million, after deducting the Underwriters’ discounts and commissions and estimated offering expenses payable by the Company.

Summary of Significant Accoun22

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and judgments that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to revenue recognition, clinical trial accruals, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results may differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity date of 90 days or less on the date of purchase to be cash equivalents. The Company invests its cash in bank deposits and money market funds.
Cash overdrafts	Cash overdrafts An overdraft totaling $1.5 million was classified as accounts payable at December 31, 2015. The Company’s policy is to report the change in overdrafts as an operating activity in the Statements of Cash Flows.
Restricted Cash	Restricted Cash The Company is required to guarantee the credit limit on its corporate credit card with a certificate of deposit of $0.1 million. The collateral will be released upon the cancellation of the corporate credit card.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. Cash and cash equivalents are invested through banks and other financial institutions in the United States. Such deposits may be in excess of insured limits. The Company maintains cash and cash equivalents and investments with various high credit quality and capitalized financial institutions.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Leasehold improvements are amortized over the lesser of the estimated useful lives or the related remaining lease term.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The carrying value of long-lived assets, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the asset may not be recoverable. An impairment loss is recognized when the total of estimated future undiscounted cash flows, expected to result from the use of the asset and its eventual disposition, are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. Through December 31, 2015, there have been no such impairment losses.
Income Taxes	Income Taxes The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized.
Revenue Recognition	Revenue Recognition Revenue from research activities made under collaboration partnership agreements are recognized as the services are provided and when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collectability is reasonably assured. Revenue generated from research and licensing agreements typically includes up-front signing or license fees, cost reimbursements, research services, minimum sublicense fees, milestone payments, and royalties on future licensees’ product sales. For revenue agreements with multiple-element arrangements, such as license and development agreements, the Company allocates revenue to each unit of accounting based on the relative selling price of each unit. When applying the relative selling price method, the Company determines the selling price for each deliverable using vendor-specific objective evidence or third-party evidence. If neither exists, the Company uses its best estimate of selling price for that deliverable. Revenue allocated is then recognized when the four basic revenue recognition criteria are met for each deliverable. The Company recognizes revenue from upfront payments ratably over the term of its estimated period of performance under the agreement which is recorded as licensing revenue. Reimbursements for development costs incurred under the Company’s license agreement with AstraZeneca are classified as collaborative development revenue. The Company recognizes cost reimbursement revenue under collaboration partnership agreements as the related research and development costs for services are rendered. Deferred revenue represents the portion of research or license payments received which has not been earned. Revenues from milestones, if they are nonrefundable and deemed substantive, are recognized upon successful accomplishment of the milestones. To the extent that non-substantive milestones are achieved and the Company has remaining performance obligations, milestones are deferred and recognized as revenue over the estimated remaining period of performance. The Company will recognize revenue associated with the non-substantive milestones upon achievement of the milestone if there are no undelivered units and it has no remaining performance obligations. The Company will account for sales-based milestones as royalties that will be recognized as revenue upon achievement of the milestone.
Stock-Based Compensation	Stock-Based Compensation The Company measures its stock-based payment awards made to employees and directors based on the estimated fair values of the awards and recognizes the compensation expense over the requisite service period. The Company has selected the Black-Scholes option-pricing model to estimate the fair value of its stock-based awards. Stock-based compensation expense is recognized using the straight-line method. Stock-based compensation expense is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company accounts for compensation expense related to stock options granted to non-employees based on the fair values estimated using the Black-Scholes model. Stock options granted to non-employees are remeasured at each reporting date until the award is vested.
Research and Development Costs	Research and Development Costs Research and development expenditures are expensed as incurred. Major components of research and development expenses consist of personnel costs, materials and supplies, and allocations of facilities-related costs, as well as fees paid to consultants and third parties that conduct certain research and development activities on the Company’s behalf. Payments made to other entities are under agreements that are generally cancelable by the Company. Nonrefundable advance payments for goods or services to be rendered in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.
Convertible Preferred Stock Warrant Liability	Convertible Preferred Stock Warrant Liability The Company accounted for freestanding warrants to purchase shares of convertible preferred stock that were contingently redeemable as liabilities in the balance sheets at their estimated fair value. Convertible preferred stock warrants were subject to remeasurement at each balance sheet date, and any change in fair value was recognized as a component of other expense, net in the statements of operations and comprehensive loss. The Company continued to adjust the carrying value of the warrants until the closing of the IPO, at which time the warrants were net exercised for shares of the Company’s common stock and the liability was reclassified to stockholders’ equity (deficit).
Comprehensive Loss	Comprehensive Loss Comprehensive loss is composed of two components: net loss and other comprehensive loss. Other comprehensive income (loss) refers to gains and losses that under GAAP are recorded as an element of stockholders’ equity (deficit), but are excluded from net loss. The Company did not record any transactions within other comprehensive income (loss) in the periods presented and, therefore, the net loss and comprehensive loss were the same for all periods presented.
Net Loss per Share	Net Loss per Share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share in the periods presented is the same as basic net loss per common share, since the effects of potentially dilutive securities are antidilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ In November 2015, the FASB issued ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) The Company has reviewed all other significant newly-issued accounting pronouncements and concluded that they either are not applicable to the Company’s operations or that no material effect is expected on its financial statements as a result of future adoption.
Fair Value Measurements	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 on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows: Level 1 – Valuations are based on quoted prices in active markets for identical assets or liabilities and readily accessible by us at the reporting date. Examples of assets and liabilities utilizing Level 1 inputs are certain money market funds, U.S. Treasuries and trading securities with quoted prices on active markets. Level 2 – Valuations based on inputs other than the quoted prices in active markets that are observable either directly or indirectly in active markets. Examples of assets and liabilities utilizing Level 2 inputs are U.S. government agency bonds, corporate bonds, commercial paper, certificates of deposit and over-the-counter derivatives. Level 3 – Valuations based on unobservable inputs in which there is little or no market data, which require us to develop our own assumptions.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Summary of Fair Value Measurements of Company's Financial Assets and Liabilities	The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy: December 31, 2015 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 105,819 $ 105,819 $ — $ — Certificates of deposit 100 — 100 — Total $ 105,919 $ 105,819 $ 100 $ — December 31, 2014 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 105,410 $ 105,410 $ — $ — Certificates of deposit 100 — 100 — Total $ 105,510 $ 105,410 $ 100 $ —

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consist of the following: December 31, 2015 2014 (in thousands) Laboratory equipment $ 4,471 $ 3,039 Office equipment and furniture 134 229 Construction in progress — 362 Leasehold improvements 3,914 2,135 Property and equipment, gross 8,519 5,765 Less: accumulated depreciation (3,808 ) (3,634 ) Total property and equipment, net $ 4,711 $ 2,131

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Summary of Activity Under 2008 Plan and 2014 Plan, Including Grants to Nonemployees and Restricted Stock Issued	The following table summarizes activity under the 2008 Plan and the 2014 Plan, including grants to nonemployees and restricted stock issued: Options Issued and Outstanding Shares Available for Number of Shares Average Exercise Aggregate (in thousands) Balance at December 31, 2012 96,841 1,293,767 $ 0.77 Options granted (99,552 ) 99,552 3.42 Options exercised — (223,865 ) 0.56 Options canceled 6,625 (6,625 ) 2.23 Balance at December 31, 2013 3,914 1,162,829 $ 1.03 Options authorized 1,452,661 — Options granted (188,888 ) 188,888 24.41 Options exercised — (336,398 ) 0.71 Options canceled 4,084 (4,084 ) 2.21 Options repurchased 3,511 (3,511 ) 0.55 Issuance of common stock for services (10,000 ) — — Balance at December 31, 2014 1,265,282 1,007,724 $ 5.51 Options authorized 743,569 — Options granted (379,709 ) 379,709 19.60 Options exercised — (77,784 ) 1.42 Options canceled 28,563 (28,563 ) 12.41 Issuance of common stock for services (13,285 ) — — Balance at December 31, 2015 1,644,420 1,281,086 $ 9.78 $ 13,129 Vested and expected to vest at December 31, 2015 1,259,972 $ 9.59 $ 13,096 Vested at December 31, 2015 835,860 $ 4.36 $ 12,075
Summary of Weighted Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan	The estimated grant date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following weighted assumptions: Year Ended December 31, 2015 2014 2013 Expected term (years) 5.89 5.97 6.07 Volatility 75 % 94 % 98 % Risk-free interest rate 1.64 % 1.79 % 1.35 % Dividend yield — % — % — %
Summary of Stock-Based Compensation Recognized	Stock-based Compensation Total stock-based compensation recognized was as follows (in thousands): Year Ended December 31, 2015 2014 2013 (in thousands) Research and development $ 1,327 $ 1,376 $ 200 General and administrative 1,307 316 152 Total stock-based compensation $ 2,634 $ 1,692 $ 352
2014 Employee Stock Purchase Plan [Member]
Summary of Weighted Average Assumptions to Estimate Fair Value of Stock Option Awards and Employee Stock Purchase Plan	The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of ESPP purchase rights granted to employees: Year Ended December 31, 2015 2015 2014 Expected term ( years) 0.5 0.5 Volatility 97 % 73 % Risk-free interest rate 0.16 % 0.05 % Dividend yield — % — %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate	The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate: December 31, 2015 2014 2013 Expected income tax provision at the federal statutory rate 35.0 % 35.0 % 35.0 % State taxes, net of federal benefit (3.8 ) 4.6 (1.4 ) Change in valuation allowance (30.7 ) (17.9 ) (22.6 ) Nondeductible expenses — (20.6 ) (20.8 ) Tax credits 1.3 — 7.3 Other (1.7 ) (3.2 ) 0.3 Income tax provision 0.1 % (2.1 %) (2.2 %)
Significant Components of the Company's Deferred Tax Assets	Significant components of the Company’s deferred tax assets are as follows: December 31, 2015 2014 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 30,572 $ 11,262 Deferred revenue — 11,099 Research credits 1,919 1,260 Other 1,582 1,201 Gross deferred tax assets 34,073 24,822 Valuation allowance (33,845 ) (24,741 ) Total deferred tax assets 228 81 Deferred tax liabilities (228 ) (81 ) Net deferred tax assets $ — $ —
Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: December 31, 2015 2014 2013 (in thousands) Balance at beginning of year $ 2,815 $ 1,411 $ 1,064 Additions (subtractions) based on tax positions related to prior year (58 ) 405 — Additions based on tax positions related to current year 541 999 347 Balance at end of year $ 3,298 $ 2,815 $ 1,411

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Computation of Net Loss Per Common Share	The following table sets forth the computation of net loss per common share (in thousands, except share and per share amounts): December 31, 2015 2014 2013 Numerator: Net loss $ (29,621 ) $ (3,214 ) $ (6,564 ) Denominator: Weighted average number of shares outstanding—basic and diluted 22,892,640 10,248,337 1,127,948 Net loss per share—basic and diluted $ (1.29 ) $ (0.31 ) $ (5.82 )
Calculation of Anti-dilutive Potentially Dilutive Securities Not Included in Diluted Per Share	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: December 31, 2015 2014 2013 Convertible preferred stock — — 11,517,222 Options to purchase common stock 1,244,442 1,007,724 1,162,829 Warrants to purchase convertible preferred stock — — 574,953 Warrants to purchase common stock 300,302 — — Total 1,544,744 1,007,724 13,255,004

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments Under the Noncancelable Operating Lease	The future minimum payments under the noncancelable operating lease at December 31, 2015, are as follows (in thousands): Year ending December 31, Amounts 2016 868 2017 895 2018 921 2019 653 Total $ 3,337

Selected Quarterly Financial 29

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Results from Operations	Selected quarterly financial results from operations for the years ended December 31, 2015 and 2014 are as follows (in thousands, except per share amounts): 2015 Quarter End March 31, June 30 September 30 December 31 Total revenue $ 5,883 $ 18,143 $ — $ — Operating expenses 9,373 9,087 18,079 16,876 Net (loss) income (3,502 ) 9,007 (18,126 ) (17,000 ) Net (loss) income per share: Basic (0.19 ) 0.43 (0.70 ) (0.65 ) Diluted (0.19 ) 0.42 (0.70 ) (0.65 ) 2014 Quarter End March 31, June 30 September 30 December 31 Total revenue $ 8,550 $ 9,137 $ 7,598 $ 6,338 Operating expenses 9,014 6,386 7,517 10,270 Net (loss) income (3,071 ) 3,753 74 (3,970 ) Net (loss) income per share: Basic (2.44 ) 0.20 — (0.21 ) Diluted (2.44 ) 0.18 — (0.21 )

Organization and Basis of Pre30

Organization and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jun. 24, 2014USD ($)shares	Jun. 18, 2014USD ($)	Jun. 30, 2015shares	Dec. 31, 2015Segment$ / sharesshares	Dec. 31, 2014USD ($)$ / sharesshares
Organization And Basis Of Presentation [Line Items]
Date of incorporation				Oct. 17, 2007
Number of operating segments | Segment				1
Place of incorporation				Delaware
Stock issued during period, shares, new issues			7,242,992
Net proceeds from the IPO | $		$ 61,200
Underwriting discounts and commissions and expenses | $		$ 7,800
Convertible preferred stock converted to common stock, value | $					$ 56,155
Shares authorized	305,000,000
Common stock, shares authorized	300,000,000			300,000,000	300,000,000
Preferred stock, shares authorized	5,000,000			5,000,000	5,000,000
Common stock, par value | $ / shares				$ 0.0001	$ 0.0001
Preferred stock, par value | $ / shares				$ 0.0001	$ 0.0001
Preferred stock, shares outstanding				0	0
Common Stock [Member]
Organization And Basis Of Presentation [Line Items]
Convertible preferred stock converted to common stock, shares	11,517,222
Convertible preferred stock converted to common stock, value | $	$ 56,200
IPO [Member]
Organization And Basis Of Presentation [Line Items]
Stock issued during period, shares, new issues	4,928,900
Additional common stock issued on exercise of option by Underwriters	642,900
IPO [Member] | Common Stock [Member]
Organization And Basis Of Presentation [Line Items]
Stock issued during period, shares, new issues					4,928,900

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Organization And Basis Of Presentation [Line Items]
Cash and cash equivalents original maturity dates	90 days or less
Overdraft Payable	$ 1,500,000
Restricted cash	100,000	$ 100,000
Impairment loss of long lived assets	$ 0
Minimum [Member]
Organization And Basis Of Presentation [Line Items]
Property and equipment, estimated useful lives	3 years
Maximum [Member]
Organization And Basis Of Presentation [Line Items]
Property and equipment, estimated useful lives	5 years

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Fair Value Measurements of Company's Financial Assets and Liabilities (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets:
Assets at fair value	$ 105,919	$ 105,510
Level 1 [Member]
Assets:
Assets at fair value	105,819	105,410
Level 2 [Member]
Assets:
Assets at fair value	100	100
Money Market Funds [Member]
Assets:
Assets at fair value	105,819	105,410
Money Market Funds [Member] | Level 1 [Member]
Assets:
Assets at fair value	105,819	105,410
Certificates of Deposit [Member]
Assets:
Assets at fair value	100	100
Certificates of Deposit [Member] | Level 2 [Member]
Assets:
Assets at fair value	$ 100	$ 100

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	Dec. 31, 2015USD ($)
Fair Value Disclosures [Abstract]
Transfer of assets from Level 1 to Level 2	$ 0
Transfer of assets from Level 2 to Level 1	$ 0

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 8,519	$ 5,765
Less: accumulated depreciation	(3,808)	(3,634)
Total property and equipment, net	4,711	2,131
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,471	3,039
Office Equipment And Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	134	229
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross		362
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,914	$ 2,135

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 0.8	$ 0.3	$ 0.6

Collaboration and Licensing A36

Collaboration and Licensing Agreements - Additional Information (Detail) - USD ($)	1 Months Ended					3 Months Ended	12 Months Ended
	Nov. 30, 2015	Sep. 30, 2015	Jun. 30, 2015	May. 31, 2014	Oct. 31, 2012	Jun. 30, 2015	Dec. 31, 2013	Dec. 31, 2015
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Payment received on termination and return of rights		$ 0
AstraZeneca [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Upfront payment received				$ 25,000,000	$ 35,000,000		$ 15,000,000
Amount of upfront payment for return of licenses			$ 15,000,000			$ 15,000,000
Percentage of royalty on net sales required to pay under the agreement			10.00%
Percentage of non-royalty revenue received			20.00%
Aggregate amount payable under termination agreement			$ 90,000,000			90,000,000
Amount of reimbursement paid for certain research and development expenses in consideration of acceleration of transfer of information and materials			10,000,000			10,000,000
Recognized deferred revenue						$ 43,100,000
Clinical trial material expenses								$ 7,300,000
AstraZeneca [Member] | Maximum [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Maximum amount of obligation to supply clinical trial materials, drug substance and drug product	$ 8,000,000		$ 10,000,000
Sanofi [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue recognized				$ 1,250,000

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 24, 2014	Dec. 31, 2014
Class of Stock [Line Items]
Convertible preferred stock converted to common stock, value		$ 56,155
Common Stock [Member]
Class of Stock [Line Items]
Convertible preferred stock converted to common stock, shares	11,517,222
Convertible preferred stock converted to common stock, value	$ 56,200

Preferred Stock Warrants - Addi

Preferred Stock Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2013	Jun. 30, 2015	Aug. 31, 2011
Class of Stock Disclosures [Abstract]
Company issued warrants			574,953
Exercise price of the warrants		$ 0.125	$ 0.09
Fair value of preferred stock warrant liability, probability of IPO scenario, percentage	20.00%
Fair value of preferred stock warrant liability, probability of merger scenario, percentage	10.00%
Fair value of preferred stock warrant liability, probability of stay private scenario, percentage	70.00%
Convertible preferred stock warrant liability	$ 6.5

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) - USD ($)	Jan. 01, 2016	Jan. 01, 2015	Jun. 18, 2014	Jan. 31, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period						4 years
Common stock reserved						1,454,549
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options			1,153,279
Weighted-average grant-date estimated fair value of options granted						$ 12.91	$ 18.53	$ 2.68
Estimated fair value of common stock						$ 18.12
Fair value of options vested during period						$ 2,400,000	$ 500,000	$ 200,000
Shares available for future grant						1,644,420	1,265,282	3,914	96,841
Stock-based compensation charge							$ 800,000
Gross proceeds from issuance of common stock					$ 77,800,000
Proceeds from issuance of common stock, net of issuance costs					$ 74,300,000	$ 74,323,000	$ 61,241,000
Common stock sold and issued					7,242,992
Purchase price of common shares					$ 10.70
Warrants issued to purchase common stock					2,172,899
Purchase price for warrants					$ 0.125					$ 0.09
Warrants exercise price per share					$ 13.91
Warrants expiration term					5 years
Warrants description						The warrants are exercisable for an exercise price of $13.91 per share at any time prior to the earlier of (i) 5 years from the date of issuance or (ii) certain changes in control of the Company.
Maximum warrants ownership percentage by each holder of warrants					9.99%
Number of warrants exercised						0
Expected dividend yield						$ 0
Options Issued and Outstanding Number of Shares, Options granted						379,709	188,888	99,552
Issuance of common stock for services (Shares)						13,285	10,000
Issuance of common stock for services, amount						$ 194,000	$ 208,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options	1,038,595
Proceeds from issuance of common stock, net of issuance costs				$ 80,400,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based award accelerated vesting number of shares							58,969
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense						$ 5,600,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period						2 years 7 months 6 days
Non Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date estimated fair value of options granted						$ 18.58	$ 20.77	$ 3.43
Stock-based compensation charge						$ 200,000	$ 100,000
Options Issued and Outstanding Number of Shares, Options granted						5,000	10,000	3,333
2014 Equity Incentive Award Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved						1,419,328
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options						10,683,053
Possible increase in shares reserved for issuance as percentage of outstanding stock						4.00%
2008 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved						35,221
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved						202,762
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options		185,892				2,230,374
Possible increase in shares reserved for issuance as percentage of outstanding stock						1.00%
Employee stock purchase plan initial offering commenced period						Sep. 1, 2014
Employee stock purchase plan initial offering ending period						Feb. 27, 2015
Number of shares authorized for issuance						388,654
Shares available for future grant						347,074
Number of shares sold under the plan						41,580	0
Weighted-average purchase price						$ 13.25
Proceeds from issuance of shares						$ 600,000
Unrecognized stock based compensation expense						$ 100,000
Unrecognized stock based compensation expense, weighted-average remaining recognition period						2 months 12 days

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Activity Under 2008 Plan and 2014 Plan, Including Grants to Nonemployees and Restricted Stock Issued (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended			18 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014
Equity [Abstract]
Shares Available for Grant, Beginning balance	1,265,282	3,914	96,841
Shares Available for Grant, Options authorized	743,569	1,452,661
Shares Available for Grant, Options granted	(379,709)	(188,888)	(99,552)
Shares Available for Grant, Options exercised	0	0	0
Shares Available for Grant, Options canceled	28,563	4,084	6,625
Shares Available for Grant, Options repurchased		3,511
Shares Available for Grant, Issuance of common stock for services	(13,285)	(10,000)
Shares Available for Grant, Ending balance	1,644,420	1,265,282	3,914	1,265,282
Options Issued and Outstanding Number of Shares, Beginning balance	1,007,724	1,162,829	1,293,767
Options Issued and Outstanding Number of Shares, Options authorized	0	0
Options Issued and Outstanding Number of Shares, Options granted	379,709	188,888	99,552
Options Issued and Outstanding Number of Shares, Options exercised	(77,784)	(336,398)	(223,865)
Options Issued and Outstanding Number, Options cancelled	(28,563)	(4,084)	(6,625)
Options Issued and Outstanding Number of Shares, Options repurchased		(3,511)
Options Issued and Outstanding Number of Shares, Issuance of common stock for services	0	0
Options Issued and Outstanding Number of Shares, Ending balance	1,281,086	1,007,724	1,162,829	1,007,724
Options Issued and Outstanding Average Exercise Price per Share, Beginning balance	$ 5.51	$ 1.03	$ 0.77
Options Issued and Outstanding Number of Shares, Expected to vest	1,259,972
Options Issued and Outstanding Average Exercise Price per Share, Options granted	$ 19.60	24.41	3.42
Options Issued and Outstanding Number of Shares, Vested	835,860
Options Issued and Outstanding Average Exercise Price per Share, Options exercised	$ 1.42	0.71	0.56
Options Issued and Outstanding Average Exercise Price per Share, Expected to vest	9.59
Options Issued and Outstanding Average Exercise Price per Share, Options canceled	12.41	2.21	2.23
Options Issued and Outstanding Average Exercise Price per Share, Vested	$ 4.36
Options Issued and Outstanding Average Exercise Price per Share, Options repurchased				$ 0.55
Aggregate Intrinsic Value, Ending balance	$ 13,129
Options Issued and Outstanding Average Exercise Price per Share, Issuance of common stock for services	$ 0	0
Aggregate Intrinsic Value, Expected to Vest	$ 13,096
Options Issued and Outstanding Average Exercise Price per Share, Ending balance	$ 9.78	$ 5.51	$ 1.03	$ 5.51
Aggregate Intrinsic Value, Vested	$ 12,075

Equity Incentive Plans - Summ41

Equity Incentive Plans - Summary of Weighted Average Assumptions to Estimate Fair value of Stock Option Awards and Employee Stock Purchase Plan (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term ( years)	5 years 10 months 21 days	5 years 11 months 19 days	6 years 26 days
Volatility	75.00%	94.00%	98.00%
Risk-free interest rate	1.64%	1.79%	1.35%
Dividend yield	0.00%	0.00%	0.00%
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term ( years)	6 months	6 months
Volatility	97.00%	73.00%
Risk-free interest rate	0.16%	0.05%
Dividend yield	0.00%	0.00%

Equity Incentive Plans - Summ42

Equity Incentive Plans - Summary of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 2,634	$ 1,692	$ 352
Research and Development [Member] | Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	1,327	1,376	200
General and Administrative [Member] | Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 1,307	$ 316	$ 152

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to the Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Expected income tax provision at the federal statutory rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	(3.80%)	4.60%	(1.40%)
Change in valuation allowance	(30.70%)	(17.90%)	(22.60%)
Nondeductible expenses		(20.60%)	(20.80%)
Tax credits	1.30%		7.30%
Other	(1.70%)	(3.20%)	0.30%
Income tax provision	0.10%	(2.10%)	(2.20%)

Income Taxes - Significant Comp

Income Taxes - Significant Components of the Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets, Net [Abstract]
Net operating loss carryforwards	$ 30,572	$ 11,262
Deferred revenue		11,099
Research credits	1,919	1,260
Other	1,582	1,201
Gross deferred tax assets	34,073	24,822
Valuation allowance	(33,845)	(24,741)
Total deferred tax assets	228	81
Deferred tax liabilities	(228)	(81)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Line Items]
Increase (decrease) in deferred tax valuation allowance	$ 9,100,000	$ (300,000)
Estimated increase in equity due to deferred tax assets upon realization	700,000
Unrecognized tax benefits that would affect the effective tax rate if recognized	3,300,000	2,800,000	$ 1,400,000
Accrued interest and penalties related to unrecognized tax benefits	0	$ 0	$ 0
Federal Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 85,200,000
Operating loss carryforward expiration year	2,030
Federal Tax Authority [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 2,700,000
Tax credit carryforward expiration year	2,027
State Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 32,300,000
Operating loss carryforward expiration year	2,030
State Tax Authority [Member] | Research and Development Tax Credit [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 3,000,000
State Tax Authority [Member] | Minimum Tax Credit Carryforward [Member]
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 200,000

Income Taxes - Reconciliation46

Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 2,815	$ 1,411	$ 1,064
Additions (subtractions) based on tax positions related to prior year	(58)	405
Additions based on tax positions related to current year	541	999	347
Balance at end of year	$ 3,298	$ 2,815	$ 1,411

Net Loss per Share - Computatio

Net Loss per Share - Computation of Net Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator:
Net loss	$ (17,000)	$ (18,126)	$ 9,007	$ (3,502)	$ (3,970)	$ 74	$ 3,753	$ (3,071)	$ (29,621)	$ (3,214)	$ (6,564)
Denominator:
Weighted average number of shares outstanding-basic and diluted									22,892,640	10,248,337	1,127,948
Net loss per share - basic and diluted									$ (1.29)	$ (0.31)	$ (5.82)

Net Loss per Share - Calculatio

Net Loss per Share - Calculation of Anti-dilutive Potentially Dilutive Securities Not Included in Diluted Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	1,544,744	1,007,724	13,255,004
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	1,244,442	1,007,724	1,162,829
Warrants to Purchase Convertible Preferred Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares			574,953
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares	300,302
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, shares			11,517,222

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Related party transactions	$ 0
Clinical Operations Consulting Arrangement [Member] | Spouse of Executive Officer [Member]
Related Party Transaction [Line Items]
Research and development service expenses		$ 200,000	$ 200,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Lease expiration date	Sep. 30, 2016
Amount provided lessor with irrevocable letter of credit		$ 100,000
Rent expense under operating leases		900,000	$ 600,000	$ 500,000
Purchase commitments		2,300,000
Amended Facility Lease Agreement [Member]
Loss Contingencies [Line Items]
Lease improvement allowance maximum amount		$ 600,000
Lease expiration date		Sep. 30, 2019

Commitments and Contingencies51

Commitments and Contingencies - Schedule of Future Minimum Payments Under the Noncancelable Operating Lease (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,016	$ 868
2,017	895
2,018	921
2,019	653
Total	$ 3,337

Selected Quarterly Financial 52

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Results from Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Total revenue			$ 18,143	$ 5,883	$ 6,338	$ 7,598	$ 9,137	$ 8,550	$ 24,026	$ 31,623	$ 28,928
Operating expenses	$ 16,876	$ 18,079	9,087	9,373	10,270	7,517	6,386	9,014	53,415	33,187	31,793
Net (loss) income	(17,000)	(18,126)	9,007	(3,502)	(3,970)	74	3,753	(3,071)	(29,621)	(3,214)	(6,564)
Net (loss) income per share:
Total revenue			18,143	5,883	6,338	7,598	9,137	8,550	24,026	31,623	28,928
Operating expenses	16,876	18,079	9,087	9,373	10,270	7,517	6,386	9,014	53,415	33,187	31,793
Net (loss) income	$ (17,000)	$ (18,126)	$ 9,007	$ (3,502)	$ (3,970)	$ 74	$ 3,753	$ (3,071)	$ (29,621)	$ (3,214)	$ (6,564)
Basic	$ (0.65)	$ (0.70)	$ 0.43	$ (0.19)	$ (0.21)		$ 0.20	$ (2.44)
Diluted	$ (0.65)	$ (0.70)	$ 0.42	$ (0.19)	$ (0.21)		$ 0.18	$ (2.44)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Jan. 31, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Sale and issuance of common stock			25,964,886	18,589,245
Net proceeds from offering		$ 74,300	$ 74,323	$ 61,241
Subsequent Event [Member]
Subsequent Event [Line Items]
Sale and issuance of common stock	8,625,000
Net proceeds from offering	$ 80,400