aTyr Pharma (ATYR) 10-Q 12 Aug 15 2015 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Aug. 07, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q2
Trading Symbol	LIFE
Entity Registrant Name	ATYR PHARMA INC
Entity Central Index Key	1,339,970
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		23,639,280

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 63,066	$ 13,899
Short-term investments	39,891	1,954
Prepaid expenses and other assets	3,218	656
Total current assets	106,175	16,509
Long-term investments	44,738
Property and equipment, net	2,022	1,925
Other assets	146	2,210
Total assets	153,081	20,644
Current liabilities:
Accounts payable	3,002	1,433
Accrued expenses	2,817	2,932
Current portion of deferred rent	305	295
Current portion of commercial bank debt	3,248	3,134
Convertible promissory note		2,000
Preferred stock warrant liabilities		319
Total current liabilities	9,372	10,113
Deferred rent, net of current portion	291	445
Commercial bank debt, net of current portion	3,489	5,142
Other long-term liabilities	$ 588	$ 335
Commitments and contingencies (Note 3)
Redeemable convertible preferred stock, $0.001 par value; authorized shares - 7,285,456 at June 30, 2015 and 75,772,871 at December 31, 2014; issued and outstanding shares - none at June 30, 2015 and 73,487,415 at December 31, 2014; liquidation preference of $0 at June 30, 2015 and $95,619 at December 31, 2014		$ 95,619
Stockholders' equity (deficit):
Common stock, $0.001 par value; authorized shares - 150,000,000 at June 30, 2015 and 95,500,000 at December 31, 2014; issued and outstanding shares - 23,639,280 at June 30, 2015 and 909,880 at December 31, 2014	$ 24	1
Additional paid-in capital	269,725	19,209
Stockholder note receivable		(69)
Accumulated other comprehensive loss	(106)
Accumulated deficit	(130,302)	(110,151)
Total stockholders' equity (deficit)	139,341	(91,010)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 153,081	$ 20,644

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock, par value	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	7,285,456	75,772,871
Redeemable convertible preferred stock, shares issued	0	73,487,415
Redeemable convertible preferred stock, shares outstanding	0	73,487,415
Redeemable convertible preferred stock, liquidation preference	$ 0	$ 95,619
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	95,500,000
Common stock, shares issued	23,639,280	909,880
Common stock, shares outstanding	23,639,280	909,880

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Operating expenses:
Research and development	$ 7,502	$ 3,638	$ 14,095	$ 8,026
General and administrative	3,396	1,725	5,725	3,267
Total operating expenses	10,898	5,363	19,820	11,293
Loss from operations	(10,898)	(5,363)	(19,820)	(11,293)
Other income (expense), net	(182)	(225)	(331)	(388)
Net loss	(11,080)	(5,588)	(20,151)	(11,681)
Accretion to redemption value of redeemable convertible preferred stock	(15)	(139)	(15)	(277)
Net loss attributable to common stockholders	$ (11,095)	$ (5,727)	$ (20,166)	$ (11,958)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.74)	$ (6.85)	$ (2.53)	$ (14.69)
Weighted average common stock shares outstanding, basic and diluted	14,901,473	836,533	7,955,973	814,030

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (11,080)	$ (5,588)	$ (20,151)	$ (11,681)
Other comprehensive loss:
Changes in unrealized loss on available-for-sale investments	(106)		(106)
Comprehensive loss	$ (11,186)	$ (5,588)	$ (20,257)	$ (11,681)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities
Net loss	$ (20,151)	$ (11,681)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	418	411
Issuance of common stock for technology	1,411
Stock-based compensation	1,419	312
Amortization of debt discount	168	155
Change in fair value of preferred stock warrant liability	(29)	85
Amortization of investment premium	192	15
Deferred rent	(144)	(136)
Loss on disposal of property and equipment	1
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,497)	(53)
Accounts payable and accrued expenses	717	(353)
Net cash used in operating activities	(17,495)	(11,245)
Cash flows from investing activities
Purchase of property and equipment	(163)	(249)
Purchases of investment securities	(84,927)	(5,397)
Maturities of investment securities	1,954
Net cash used in investing activities	(83,136)	(5,646)
Cash flows from financing activities
Issuance of preferred stock for cash, net of issuance costs	75,617
Issuance of common stock through initial public offering, net of offering costs	77,246
Proceeds from issuance of common stock through option exercises	533	70
Proceeds from notes payable to bank		5,000
Repayments on notes payable to bank	(1,598)
Repayment of convertible debt	(2,000)
Net cash provided by financing activities	149,798	5,070
Net change in cash and cash equivalents	49,167	(11,821)
Cash and cash equivalents at beginning of the period	13,899	36,457
Cash and cash equivalents at end of the period	63,066	$ 24,636
Supplemental schedule of noncash investing and financing activities
Initial public offering costs included in accounts payable	$ 344

Organization, Business, Basis o

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies	1. Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies Organization and Business aTyr Pharma, Inc. (the Company) was incorporated in the state of Delaware on September 8, 2005. The Company is focused on the discovery and clinical development of innovative medicines for patients suffering from severe rare diseases. Initial Public Offering On May 12, 2015, the Company completed its initial public offering (IPO) of 6,164,000 shares of common stock at $14.00 per share, resulting in gross proceeds of approximately $86.3 million and net proceeds of $75.9 million, after underwriting and other expenses of approximately $10.4 million (consisting of approximately $6.0 million in underwriting discounts and commissions and approximately $4.4 million in other offering expenses). In connection with the IPO, all outstanding shares of redeemable convertible preferred stock were converted into 16,279,859 shares of the Company’s common stock and warrants to purchase 206,581 shares of redeemable convertible preferred stock were converted into warrants to purchase 25,970 shares of the Company’s common stock with a resultant reclassification of the warrant liabilities to additional paid-in capital. In addition, the Company filed an amended and restated certificate of incorporation on May 12, 2015, authorizing 150,000,000 shares of common stock and 7,285,456 shares of preferred stock, 5,000,000 of which is undesignated preferred stock. Upon the closing of the IPO, 1,574,566 shares of common stock were reserved for future issuance under the 2015 Stock Option and Incentive Plan (the 2015 Plan) and 227,623 shares of common stock were reserved for future issuance under the 2015 Employee Stock Purchase Plan (the 2015 ESPP). Principles of Consolidation The consolidated financial statements include the accounts of aTyr Pharma, Inc., its 98% majority-owned subsidiary in Hong Kong, Pangu BioPharma Limited (Pangu BioPharma), and six variable interest entities (Affiliates), in which aTyr Pharma, Inc. was considered to be the primary beneficiary. The Affiliates were dissolved in the fourth quarter of 2014 and the Company continued the operating activities of the Affiliates. All intercompany transactions and balances are eliminated in consolidation. Reverse Stock Split On May 5, 2015, the Company filed an amendment to its amended and restated certificate of incorporation to effect a one-for-7.95413 reverse stock split of the Company’s common stock (the Reverse Stock Split). The par value and the authorized shares of the common and convertible preferred stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock and the conversion ratio of the redeemable convertible preferred stock have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented. Unaudited Interim Financial Information The accompanying interim condensed consolidated financial statements are unaudited. These unaudited interim financial statements have been prepared in accordance with United States generally accepted accounting principles (GAAP) and following the requirements of the United States Securities and Exchange Commission (SEC) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. In management’s opinion, the unaudited interim financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position and its results of operations and its cash flows for periods presented. These statements do not include all disclosures required by GAAP and should be read in conjunction with the Company’s financial statements and accompanying notes for the fiscal year ended December 31, 2014, contained in the Company’s final prospectus dated May 6, 2015 filed by the Company with the SEC on May 7, 2015 pursuant to Rule 424(b) under the Securities Act of 1933, as amended (the Securities Act), in connection with the Company’s IPO. The results of the interim periods are not necessarily indicative of the results expected for the full fiscal year or any other interim period or any future year or period. Use of Estimates The Company’s consolidated financial statements are prepared in accordance with GAAP. The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the fair value of equity issuances and awards, and clinical trials and research and development expense accruals. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately differ materially from these estimates and assumptions. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted average number of common shares outstanding that are subject to repurchase. The Company has excluded 65,351 and 66,830 shares subject to repurchase from the weighted average number of common shares outstanding for the three months ended June 30, 2015 and 2014, respectively. The Company has excluded 68,886 and 67,354 shares subject to repurchase from the weighted average number of common shares outstanding for the six months ended June 30, 2015 and 2014, respectively. Diluted net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common stock equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of redeemable convertible preferred stock, redeemable convertible preferred stock issuable upon conversion of convertible promissory note, warrants for the purchase of redeemable convertible preferred stock, warrants for common stock and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common share equivalents): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 Redeemable convertible preferred stock outstanding — 9,238,868 — 9,238,868 Redeemable convertible preferred stock issuable upon conversion of convertible promissory note — 94,455 — 94,455 Warrants for redeemable convertible preferred stock — 25,970 — 25,970 Warrants for common stock 25,970 — 25,970 — Common stock options 1,164,140 1,085,257 1,164,140 1,085,257 1,190,110 10,444,550 1,190,110 10,444,550

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	2. Fair Value Measurements The carrying amounts of cash equivalents, prepaid and other assets, accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. Based on the borrowing rates currently available to the Company for loans with similar terms, which is considered a Level 2 input, the Company believes that the fair value of its commercial bank debt and convertible promissory notes approximate their carrying values. Investment securities and preferred stock warrant liabilities are recorded at fair value. The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. Financial assets measured at fair value on a recurring basis consist of investment securities. Investment securities are recorded at fair value, defined as the exit price in the principal market in which the Company would transact, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Level 2 securities are valued using quoted market prices for similar instruments, non-binding market prices that are corroborated by observable market data, or discounted cash flow techniques and include the Company’s investments in corporate debt securities and commercial paper. Financial liabilities measured at fair value on a recurring basis include the Company’s preferred stock warrant liabilities. None of the Company’s non-financial assets and liabilities is recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. Assets and liabilities measured at fair value on a recurring basis are as follows (in thousands): Fair Value Measurements Using Quoted Prices in Significant Significant As of June 30, 2015: Assets: Current: Cash and cash equivalents $ 63,066 $ 63,066 $ — $ — Short-term investments - Corporate debt securities 39,891 — 39,891 — Long-term investments: Agency bonds 7,072 — 7,072 — US treasury debt securities 7,505 — 7,505 — Asset-backed securities 9,869 — 9,869 — Corporate debt securities 20,292 — 20,292 — Sub-total long-term investments 44,738 — 44,738 — Total assets measured at fair value $ 147,695 $ 63,066 $ 84,629 $ — As of December 31, 2014: Assets: Cash and cash equivalents $ 13,899 $ 13,899 $ — $ — Short-term investments - Corporate debt securities 1,954 — 1,954 — Total assets measured at fair value $ 15,853 $ 13,899 $ 1,954 $ — Liabilities: Preferred stock warrant liabilities $ 319 $ — $ — $ 319 At June 30, 2015 and December 31, 2014 available-for-sale investments are detailed as follows (in thousands): June 30, 2015 Gross Gross Gross Market Value Short-term investments: Corporate debt securities $ 39,944 $ 2 $ (55 ) $ 39,891 Long-term investments: Agency bonds 7,075 — (3 ) 7,072 US treasury debt securities 7,503 2 — 7,505 Asset-backed securities 9,874 — (5 ) 9,869 Corporate debt securities 20,339 — (47 ) 20,292 $ 44,791 $ 2 $ (55 ) $ 44,738 December 31, 2014 Gross Gross Gross Market Value Short-term: Corporate debt securities $ 1,954 $ — $ — $ 1,954 Available-for-sale investments that are in an unrealized loss position at June 30, 2015 are as follows (in thousands): Estimated Fair Gross Unrealized Agency bonds $ 7,072 $ (3 ) Asset-backed securities 6,005 (5 ) Corporate debt securities 56,234 (102 ) $ 69,311 $ (110 ) As of June 30, 2015, all available-for-sale investments have contractual maturity dates within two years. At each reporting date, the Company performs an evaluation of impairment to determine if the unrealized losses are other-than-temporary. Factors considered in determining whether a loss is other-than-temporary include the length of time and extent to which fair value has been less than the cost basis, the financial condition of the issuer, and the Company’s intent and ability to hold the investment until recovery of its amortized cost basis. The Company intends, and has the ability, to hold its investments in unrealized loss positions until their amortized cost basis has been recovered. Based on its evaluation, the Company determined that its unrealized losses were not other-than-temporary at June 30, 2015. All warrant liabilities are recorded at fair value utilizing the Black-Scholes option pricing model using significant unobservable inputs consistent with the inputs used for the Company’s stock-based compensation expense adjusted for the warrants’ expected life. The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands): Warrant Balance at December 31, 2014 $ 319 Change in fair value (29 ) Balance at May 5, 2015 $ 290 Reclassification to additional paid-in capital as of IPO on May 6, 2015 (290 ) Balance at June 30, 2015 $ —

Debt, Commitments and Contingen

Debt, Commitments and Contingencies	6 Months Ended
	Jun. 30, 2015
Text Block [Abstract]
Debt, Commitments and Contingencies	3. Debt, Commitments and Contingencies Commercial Bank Debt Commercial bank debt and unamortized discount balances are as follows (in thousands): June 30, December 31, Commercial bank debt $ 6,842 $ 8,439 Less debt discount, net of current portion (26 ) (60 ) Commercial bank debt, net of debt discount 6,816 8,379 Less current portion of commercial bank debt (3,327 ) (3,237 ) Commercial bank debt, net of current portion $ 3,489 $ 5,142 Current portion of commercial bank debt $ 3,327 $ 3,237 Current portion of debt discount (79 ) (103 ) Current portion of commercial bank debt $ 3,248 $ 3,134 Future minimum principal and interest payments under the Company’s loan and security agreement with Silicon Valley Bank, including the final payment, are as follows (in thousands): As of June 30, 2015 $ 1,811 2016 3,622 2017 2,310 7,743 Less interest and final payment (901 ) Commercial bank debt $ 6,842 Facility Lease In December 2011, the Company entered into a noncancelable operating lease that included certain tenant improvement allowances and is subject to base lease payments, which escalate over the term of the lease, additional charges for common area maintenance and other costs. The lease expires in May 2017 and the Company has an option to extend the lease for a period of five years. Rent expense for the three months ended June 30, 2015 and 2014 was $0.1 million. Rent expense for the six months ended June 30, 2015 and 2014 was $0.2 million and $0.1 million, respectively. In conjunction with this lease, the Company borrowed $2.0 million under a subordinated unsecured convertible promissory note issued to the venture arm of its landlord. The convertible promissory note carried an annual interest rate of 8.0% and matured at the earlier of (i) May 2015, (ii) a liquidation event, or (iii) the closing of an initial firm commitment underwritten public offering of the Company’s common stock pursuant to a registration statement under the Act, at which time all outstanding principal and accrued interest amounts would be due, unless previously converted. In May 2015, the $2.0 million outstanding principal balance of the convertible promissory note and the $0.5 million accrued interest on the convertible promissory note was repaid in full in connection with the Company’s IPO. Future minimum payments under the non-cancelable operating lease as of June 30, 2015 were as follows (in thousands): Operating 2015 $ 299 2016 610 2017 231 $ 1,140 Research Agreements and Funding Obligations In October 2007, the Company entered into a research funding and option agreement for certain technologies from The Scripps Research Institute (TSRI). Under the agreement, the Company provides funding to TSRI to conduct certain research activities. The agreement renews automatically for successive 12 month periods starting on May 31st of each year unless the Company provides 30 days’ prior written notice to terminate the agreement. TSRI has the right to terminate the agreement if the Company fails to make any payment under the agreement or for breach or insolvency. Under the research funding and option agreement, TSRI has granted the Company options to enter into license agreements to acquire rights and exclusive licenses to develop, make, have made, use, have used, import, have imported, offer to sell, sell, and have sold certain licensed products, processes and services based on certain technology arising from the sponsored research activities. Pursuant to the terms of these license agreements, TSRI is entitled to receive tiered royalties as a percentage of net sales and a percentage of nonroyalty revenue the Company may receive from its sublicensees or partners, with the amount owed decreasing if it enters into the applicable sublicense or partnering agreement after meeting a specified clinical milestone. In addition, the Company is obligated to pay TSRI up to an aggregate of $2.75 million under each license agreement upon the achievement of specific clinical and regulatory milestone events. In January 2015, the Company and TSRI entered into an amended and restated research funding and option agreement pursuant to which the Company agreed to issue 119,840 shares of its common stock to TSRI in consideration for the adjustment of sublicense payments and the assignment of certain intellectual property rights by TSRI to the Company. The $1.4 million fair value of the common stock issued to TSRI was recorded to research and development expense. The Company issued the shares of common stock to TSRI on March 31, 2015. During the three months ended June 30, 2015 and 2014, excluding the fair value of the common stock issued to TSRI described above, the Company recognized expense under the agreement in the amount of $0.2 million. During the six months ended June 30, 2015 and 2014, excluding the fair value of the common stock issued to TSRI described above, the Company recognized expense under the agreement in the amount of $0.3 million. A member of the Company’s board of directors is a faculty member at TSRI and such payments fund a portion of his research activities conducted at TSRI. During the three months ended June 30, 2015 and 2014, the Company provided charitable donations to the National Foundation for Cancer Research of $0.1 million. During the six months ended June 30, 2015 and 2014, the Company provided charitable donations to the National Foundation for Cancer Research of $0.2 million. The Company has requested that the donations be restricted to certain basic research in cancer biology and therapeutics, a portion of which funds research activities conducted at TSRI in the laboratory of a member of the Company’s board of directors. FUJIFILM Diosynth Biotechnologies U.S.A., Inc. Agreement On June 16, 2015, the Company entered into a Master Services Agreement (the MSA) with FUJIFILM Diosynth Biotechnologies U.S.A., Inc. (Fujifilm) to complete the development of the manufacturing process and for the production of the active pharmaceutical ingredient for Resolaris. Pursuant to the MSA, Fujifilm will provide the active ingredient for Resolaris to support future clinical trials, including potential pivotal trials. Under the initial scope of work executed pursuant to the MSA, Fujifilm will conduct process optimization, scale-up and demonstration, and cGMP manufacturing of the active pharmaceutical ingredient of Resolaris, and the Company is required to pay Fujifilm based on development and production milestones up to the total payment in the mid seven figures. During the three and six months ended June 30, 2015, expenses associated with this agreement were not material.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2015
Equity [Abstract]
Stockholders' Equity	4. Stockholders’ Equity Stock Option and Incentive Plans The 2015 Plan became effective upon the effectiveness of the registration statement for the IPO in May 2015, and the Company ceased granting stock options under its 2014 Stock Plan (the 2014 Plan) upon the IPO. Stock option activity is summarized as follows: Number of Weighted Balance at December 31, 2014 1,514,471 $ 4.60 Granted 1,050,045 $ 11.35 Exercised (166,454 ) $ 2.87 Canceled (2,774 ) $ 4.25 Balance at June 30, 2015 2,395,288 $ 7.70 The allocation of stock-based compensation for all options and restricted stock awards is as follows (in thousands): Three Months Ended Six Months Ended 2015 2014 2015 2014 Research and development $ 441 $ 50 $ 796 $ 93 General and administrative 375 115 623 219 $ 816 $ 165 $ 1,419 $ 312 The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Three Months Ended Six Months Ended 2015 2014 2015 2014 Expected term (in years) 5.77 – 6.08 N/A 5.77 – 6.08 6.52 – 6.56 Risk-free interest rate 1.47%-1.78 % N/A 1.47%-1.78 % 2.14 % Expected volatility 81.60%-88.10 % N/A 81.60%-100.9 % 111.1 % Expected dividend yield 0.0% N/A 0.0% 0.0% Approval of 2015 Plan On April 25, 2015, the Company’s board of directors adopted, and the Company’s stockholders approved, the 2015 Plan. The 2015 Plan became effective on May 6, 2015. A total of 1,574,566 shares of the Company’s common stock were initially reserved for issuance under the 2015 Plan. In addition, the number of shares reserved and available for issuance under the 2015 Plan will automatically increase each January 1, beginning on January 1, 2016 and thereafter until January 1, 2019, by the lesser of (i) 1,840,000 shares, (ii) 4% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or (iii) an amount determined by the Company’s board of directors. Shares underlying any awards under the 2015 Plan and any awards granted under the 2014 Plan prior to the Company’s IPO that are forfeited, canceled, reacquired by us prior to vesting, satisfied without the issuance of stock or otherwise terminated (other than by exercise) will be added to shares available for issuance under the 2015 Plan. Approval of the Employee Stock Purchase Plan On April 25, 2015, the Company’s board of directors adopted, and the Company’s stockholders approved, the Company’s 2015 Employee Stock Purchase Plan (the 2015 ESPP). The 2015 ESPP became effective on May 6, 2015. A total of 227,623 shares of the Company’s common stock were initially reserved for issuance under the 2015 ESPP. In addition, the number of shares reserved and available for purchase under the 2015 ESPP will automatically increase each January 1, beginning on January 1, 2016 and thereafter until January 1, 2019, by 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or such lesser number of shares as determined by the administrator of the 2015 ESPP. Sale of Series E Redeemable Convertible Preferred Stock On March 31, 2015, pursuant to a Series E stock purchase agreement, the Company issued an aggregate of 68,166,894 shares of its Series E redeemable convertible preferred stock at a purchase price of $1.119 per share, for aggregate cash consideration of $76.3 million and incurred $0.6 million of issuance costs. Each share of Series E redeemable convertible preferred stock was convertible into 0.12572 shares of the Company’s common stock. The purchase agreement also included an automatic conversion into approximately 0.10329 shares of common stock for each share of Series E redeemable convertible preferred stock upon completion of a qualified public offering on or before March 1, 2016. A qualified public offering must have resulted in listing on a U.S. national securities exchange and at least $50.0 million of gross proceeds at a per share price of not less than $13.00. On May 12, 2015, all outstanding shares of the Company’s redeemable convertible preferred stock converted into 7,040,991 shares of the Company’s common stock in connection with the Company’s IPO. Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows: June 30, December 31, Conversion of redeemable convertible preferred stock — 9,238,868 Conversion of redeemable convertible preferred stock issuable upon conversion of promissory note — 94,455 Redeemable convertible preferred stock warrants — 25,970 Common stock warrants 25,970 — Common stock options outstanding 2,395,288 1,514,471 Shares available under the 2015 Plan 1,164,140 180,190 Shares available under the 2015 ESPP Plan 227,623 — 3,813,021 11,053,954

Organization, Business, Basis11

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Organization and Business	Organization and Business aTyr Pharma, Inc. (the Company) was incorporated in the state of Delaware on September 8, 2005. The Company is focused on the discovery and clinical development of innovative medicines for patients suffering from severe rare diseases.
Initial Public Offering	Initial Public Offering On May 12, 2015, the Company completed its initial public offering (IPO) of 6,164,000 shares of common stock at $14.00 per share, resulting in gross proceeds of approximately $86.3 million and net proceeds of $75.9 million, after underwriting and other expenses of approximately $10.4 million (consisting of approximately $6.0 million in underwriting discounts and commissions and approximately $4.4 million in other offering expenses). In connection with the IPO, all outstanding shares of redeemable convertible preferred stock were converted into 16,279,859 shares of the Company’s common stock and warrants to purchase 206,581 shares of redeemable convertible preferred stock were converted into warrants to purchase 25,970 shares of the Company’s common stock with a resultant reclassification of the warrant liabilities to additional paid-in capital. In addition, the Company filed an amended and restated certificate of incorporation on May 12, 2015, authorizing 150,000,000 shares of common stock and 7,285,456 shares of preferred stock, 5,000,000 of which is undesignated preferred stock. Upon the closing of the IPO, 1,574,566 shares of common stock were reserved for future issuance under the 2015 Stock Option and Incentive Plan (the 2015 Plan) and 227,623 shares of common stock were reserved for future issuance under the 2015 Employee Stock Purchase Plan (the 2015 ESPP).
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of aTyr Pharma, Inc., its 98% majority-owned subsidiary in Hong Kong, Pangu BioPharma Limited (Pangu BioPharma), and six variable interest entities (Affiliates), in which aTyr Pharma, Inc. was considered to be the primary beneficiary. The Affiliates were dissolved in the fourth quarter of 2014 and the Company continued the operating activities of the Affiliates. All intercompany transactions and balances are eliminated in consolidation.
Reverse Stock Split	Reverse Stock Split On May 5, 2015, the Company filed an amendment to its amended and restated certificate of incorporation to effect a one-for-7.95413 reverse stock split of the Company’s common stock (the Reverse Stock Split). The par value and the authorized shares of the common and convertible preferred stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock and the conversion ratio of the redeemable convertible preferred stock have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying interim condensed consolidated financial statements are unaudited. These unaudited interim financial statements have been prepared in accordance with United States generally accepted accounting principles (GAAP) and following the requirements of the United States Securities and Exchange Commission (SEC) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. In management’s opinion, the unaudited interim financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position and its results of operations and its cash flows for periods presented. These statements do not include all disclosures required by GAAP and should be read in conjunction with the Company’s financial statements and accompanying notes for the fiscal year ended December 31, 2014, contained in the Company’s final prospectus dated May 6, 2015 filed by the Company with the SEC on May 7, 2015 pursuant to Rule 424(b) under the Securities Act of 1933, as amended (the Securities Act), in connection with the Company’s IPO. The results of the interim periods are not necessarily indicative of the results expected for the full fiscal year or any other interim period or any future year or period.
Use of Estimates	Use of Estimates The Company’s consolidated financial statements are prepared in accordance with GAAP. The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the fair value of equity issuances and awards, and clinical trials and research and development expense accruals. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately differ materially from these estimates and assumptions.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted average number of common shares outstanding that are subject to repurchase. The Company has excluded 65,351 and 66,830 shares subject to repurchase from the weighted average number of common shares outstanding for the three months ended June 30, 2015 and 2014, respectively. The Company has excluded 68,886 and 67,354 shares subject to repurchase from the weighted average number of common shares outstanding for the six months ended June 30, 2015 and 2014, respectively. Diluted net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted average number of common stock equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of redeemable convertible preferred stock, redeemable convertible preferred stock issuable upon conversion of convertible promissory note, warrants for the purchase of redeemable convertible preferred stock, warrants for common stock and options outstanding under the Company’s stock option plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common share equivalents): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 Redeemable convertible preferred stock outstanding — 9,238,868 — 9,238,868 Redeemable convertible preferred stock issuable upon conversion of convertible promissory note — 94,455 — 94,455 Warrants for redeemable convertible preferred stock — 25,970 — 25,970 Warrants for common stock 25,970 — 25,970 — Common stock options 1,164,140 1,085,257 1,164,140 1,085,257 1,190,110 10,444,550 1,190,110 10,444,550

Organization, Business, Basis12

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share	Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common share equivalents): Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 Redeemable convertible preferred stock outstanding — 9,238,868 — 9,238,868 Redeemable convertible preferred stock issuable upon conversion of convertible promissory note — 94,455 — 94,455 Warrants for redeemable convertible preferred stock — 25,970 — 25,970 Warrants for common stock 25,970 — 25,970 — Common stock options 1,164,140 1,085,257 1,164,140 1,085,257 1,190,110 10,444,550 1,190,110 10,444,550

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	Assets and liabilities measured at fair value on a recurring basis are as follows (in thousands): Fair Value Measurements Using Quoted Prices in Significant Significant As of June 30, 2015: Assets: Current: Cash and cash equivalents $ 63,066 $ 63,066 $ — $ — Short-term investments - Corporate debt securities 39,891 — 39,891 — Long-term investments: Agency bonds 7,072 — 7,072 — US treasury debt securities 7,505 — 7,505 — Asset-backed securities 9,869 — 9,869 — Corporate debt securities 20,292 — 20,292 — Sub-total long-term investments 44,738 — 44,738 — Total assets measured at fair value $ 147,695 $ 63,066 $ 84,629 $ — As of December 31, 2014: Assets: Cash and cash equivalents $ 13,899 $ 13,899 $ — $ — Short-term investments - Corporate debt securities 1,954 — 1,954 — Total assets measured at fair value $ 15,853 $ 13,899 $ 1,954 $ — Liabilities: Preferred stock warrant liabilities $ 319 $ — $ — $ 319
Schedule of Available-for-sale Investments	At June 30, 2015 and December 31, 2014 available-for-sale investments are detailed as follows (in thousands): June 30, 2015 Gross Gross Gross Market Value Short-term investments: Corporate debt securities $ 39,944 $ 2 $ (55 ) $ 39,891 Long-term investments: Agency bonds 7,075 — (3 ) 7,072 US treasury debt securities 7,503 2 — 7,505 Asset-backed securities 9,874 — (5 ) 9,869 Corporate debt securities 20,339 — (47 ) 20,292 $ 44,791 $ 2 $ (55 ) $ 44,738 December 31, 2014 Gross Gross Gross Market Value Short-term: Corporate debt securities $ 1,954 $ — $ — $ 1,954
Schedule of Available-for-sale Investments in Unrealized Loss Position	Available-for-sale investments that are in an unrealized loss position at June 30, 2015 are as follows (in thousands): Estimated Fair Gross Unrealized Agency bonds $ 7,072 $ (3 ) Asset-backed securities 6,005 (5 ) Corporate debt securities 56,234 (102 ) $ 69,311 $ (110 )
Schedule of Reconciliation of All Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs	The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands): Warrant Balance at December 31, 2014 $ 319 Change in fair value (29 ) Balance at May 5, 2015 $ 290 Reclassification to additional paid-in capital as of IPO on May 6, 2015 (290 ) Balance at June 30, 2015 $ —

Debt, Commitments and Conting14

Debt, Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2015
Text Block [Abstract]
Schedule of Commercial Bank Debt and Unamortized Discount	Commercial bank debt and unamortized discount balances are as follows (in thousands): June 30, December 31, Commercial bank debt $ 6,842 $ 8,439 Less debt discount, net of current portion (26 ) (60 ) Commercial bank debt, net of debt discount 6,816 8,379 Less current portion of commercial bank debt (3,327 ) (3,237 ) Commercial bank debt, net of current portion $ 3,489 $ 5,142 Current portion of commercial bank debt $ 3,327 $ 3,237 Current portion of debt discount (79 ) (103 ) Current portion of commercial bank debt $ 3,248 $ 3,134
Schedule of Future Minimum Principal and Interest Payments under Loan and Security Agreement Silicon Valley Bank Including Final Payment	Future minimum principal and interest payments under the Company’s loan and security agreement with Silicon Valley Bank, including the final payment, are as follows (in thousands): As of June 30, 2015 $ 1,811 2016 3,622 2017 2,310 7,743 Less interest and final payment (901 ) Commercial bank debt $ 6,842
Schedule of Future Minimum Payments under Non-cancelable Operating Lease	Future minimum payments under the non-cancelable operating lease as of June 30, 2015 were as follows (in thousands): Operating 2015 $ 299 2016 610 2017 231 $ 1,140

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2015
Equity [Abstract]
Summary of Stock Option Activity	Stock option activity is summarized as follows: Number of Weighted Balance at December 31, 2014 1,514,471 $ 4.60 Granted 1,050,045 $ 11.35 Exercised (166,454 ) $ 2.87 Canceled (2,774 ) $ 4.25 Balance at June 30, 2015 2,395,288 $ 7.70
Schedule of Allocation of Stock-Based Compensation for All Options and Restricted Stock Awards	The allocation of stock-based compensation for all options and restricted stock awards is as follows (in thousands): Three Months Ended Six Months Ended 2015 2014 2015 2014 Research and development $ 441 $ 50 $ 796 $ 93 General and administrative 375 115 623 219 $ 816 $ 165 $ 1,419 $ 312
Summary of Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Employee Stock Option Grants	The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Three Months Ended Six Months Ended 2015 2014 2015 2014 Expected term (in years) 5.77 – 6.08 N/A 5.77 – 6.08 6.52 – 6.56 Risk-free interest rate 1.47%-1.78 % N/A 1.47%-1.78 % 2.14 % Expected volatility 81.60%-88.10 % N/A 81.60%-100.9 % 111.1 % Expected dividend yield 0.0% N/A 0.0% 0.0%
Summary of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows: June 30, December 31, Conversion of redeemable convertible preferred stock — 9,238,868 Conversion of redeemable convertible preferred stock issuable upon conversion of promissory note — 94,455 Redeemable convertible preferred stock warrants — 25,970 Common stock warrants 25,970 — Common stock options outstanding 2,395,288 1,514,471 Shares available under the 2015 Plan 1,164,140 180,190 Shares available under the 2015 ESPP Plan 227,623 — 3,813,021 11,053,954

Organization, Business, Basis16

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Thousands	May. 12, 2015USD ($)$ / sharesshares	Jun. 30, 2015Entity$ / sharesshares	Jun. 30, 2014shares	Jun. 30, 2015USD ($)Entity$ / sharesshares	Jun. 30, 2014shares	Apr. 25, 2015shares	Dec. 31, 2014$ / sharesshares
Description Of Business [Line Items]
Common stock, Initial Public Offering price per share | $ / shares		$ 0.001		$ 0.001			$ 0.001
Net proceeds | $				$ 77,246
Common stock, shares authorized		150,000,000		150,000,000			95,500,000
Common stock reserved for future issuance		3,813,021		3,813,021			11,053,954
Number of variable interest entities | Entity		6		6
Reverse stock split of company's common stock				On May 5, 2015, the Company filed an amendment to its amended and restated certificate of incorporation to effect a one-for-7.95413 reverse stock split of the Company's common stock (the Reverse Stock Split). The par value and the authorized shares of the common and convertible preferred stock were not adjusted as a result of the Reverse Stock Split.
Ratio of reverse stock split of company's common stock				7.95413
Weighted average shares subject to repurchase		65,351	66,830	68,886	67,354
Redeemable Convertible Preferred Stock Outstanding [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance							9,238,868
2015 ESPP Plan [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance		227,623		227,623
IPO [Member]
Description Of Business [Line Items]
Issuance of common stock (shares)	6,164,000
Common stock, Initial Public Offering price per share | $ / shares	$ 14
Gross proceeds | $	$ 86,300
Net proceeds | $	75,900
Underwriting and other expenses | $	10,400
Underwriting discounts and commissions | $	6,000
Other offering expenses | $	$ 4,400
IPO [Member] | Amended and Restated Certificate of Incorporation [Member]
Description Of Business [Line Items]
Common stock, shares authorized	150,000,000
Preferred stock, shares authorized	7,285,456
IPO [Member] | Redeemable Convertible Preferred Stock Outstanding [Member]
Description Of Business [Line Items]
Shares issued upon conversion	16,279,859
IPO [Member] | Undesignated Preferred Stock [Member] | Amended and Restated Certificate of Incorporation [Member]
Description Of Business [Line Items]
Preferred stock, shares authorized	5,000,000
IPO [Member] | Warrant Equity [Member] | Redeemable Convertible Preferred Stock Outstanding [Member]
Description Of Business [Line Items]
Warrants issued upon conversion	206,581
IPO [Member] | 2015 Stock Option and Incentive Plan [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance						1,574,566
IPO [Member] | 2015 ESPP Plan [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance						227,623
Common Stock [Member] | IPO [Member] | Warrant Equity [Member] | Warrant Liabilities [Member]
Description Of Business [Line Items]
Warrants issued upon conversion	25,970
Pangu BioPharma [Member] | Hong Kong [Member]
Description Of Business [Line Items]
Majority-owned subsidiary percentage		98.00%		98.00%

Organization, Business, Basis17

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Schudule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	1,190,110	10,444,550	1,190,110	10,444,550
Redeemable Convertible Preferred Stock Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share		9,238,868		9,238,868
Redeemable Convertible Preferred Stock Issuable upon Conversion of Convertible Promissory Note [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share		94,455		94,455
Redeemable Convertible Preferred Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share		25,970		25,970
Warrants for Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	25,970		25,970
Common Stock Options Granted and Outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	1,164,140	1,085,257	1,164,140	1,085,257

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 63,066	$ 13,899
Total assets measured at fair value	147,695	15,853
Preferred Stock Warrant Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value		319
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	63,066	13,899
Total assets measured at fair value	63,066	13,899
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured at fair value	84,629	1,954
Significant Unobservable Inputs (Level 3) [Member] | Preferred Stock Warrant Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured at fair value		319
Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	39,891	1,954
Short-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	39,891	$ 1,954
Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	44,738
Long-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	20,292
Long-term Investments [Member] | Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	7,072
Long-term Investments [Member] | US Treasury Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	7,505
Long-term Investments [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	9,869
Long-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	44,738
Long-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	20,292
Long-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	7,072
Long-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | US Treasury Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	7,505
Long-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	$ 9,869

Fair Value Measurements - Sch19

Fair Value Measurements - Schedule of Available-for-sale Investments (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Short-term Investments [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	$ 39,944	$ 1,954
Gross Unrealized Gains	2
Gross Unrealized Losses	(55)
Market Value	39,891	$ 1,954
Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	44,791
Gross Unrealized Gains	2
Gross Unrealized Losses	(55)
Market Value	44,738
Long-term Investments [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	20,339
Gross Unrealized Losses	(47)
Market Value	20,292
Long-term Investments [Member] | Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	7,075
Gross Unrealized Losses	(3)
Market Value	7,072
Long-term Investments [Member] | US Treasury Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	7,503
Gross Unrealized Gains	2
Market Value	7,505
Long-term Investments [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	9,874
Gross Unrealized Losses	(5)
Market Value	$ 9,869

Fair Value Measurements - Sch20

Fair Value Measurements - Schedule of Available-for-sale Investments in Unrealized Loss Position (Detail) - Jun. 30, 2015 - USD ($) $ in Thousands	Total
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 69,311
Gross Unrealized Losses	(110)
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	7,072
Gross Unrealized Losses	(3)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	6,005
Gross Unrealized Losses	(5)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	56,234
Gross Unrealized Losses	$ (102)

Fair value Measurements - Addit

Fair value Measurements - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Available-for-sale investments contractual maturity period	2 years

Fair Value Measurements - Sch22

Fair Value Measurements - Schedule of Reconciliation of All Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs (Detail) - Warrant Liabilities [Member] - USD ($) $ in Thousands	2 Months Ended	4 Months Ended
	Jun. 30, 2015	May. 05, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 290	$ 319
Reclassification to additional paid-in capital as of IPO on May 6, 2015	$ (290)
Change in fair value		(29)
Ending balance		$ 290

Debt, Commitments and Conting23

Debt, Commitments and Contingencies - Schedule of Commercial Bank Debt and Unamortized Discount (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Commercial bank debt, net of current portion	$ 3,489	$ 5,142
Current portion of commercial bank debt	3,248	3,134
Commercial Bank Debt [Member]
Debt Instrument [Line Items]
Commercial bank debt	6,842	8,439
Less debt discount, net of current portion	(26)	(60)
Commercial bank debt, net of debt discount	6,816	8,379
Current portion of commercial bank debt	(3,327)	(3,237)
Commercial bank debt, net of current portion	3,489	5,142
Commercial bank debt, net of debt discount	6,816	8,379
Current portion of commercial bank debt	3,327	3,237
Current portion of debt discount	(79)	(103)
Current portion of commercial bank debt	$ 3,248	$ 3,134

Debt, Commitments and Conting24

Debt, Commitments and Contingencies - Schedule of Future Minimum Principal and Interest Payments under Loan and Security Agreement Silicon Valley Bank Including Final Payment (Detail) - Silicon Valley Bank [Member] $ in Thousands	Jun. 30, 2015USD ($)
Debt Instrument [Line Items]
2,015	$ 1,811
2,016	3,622
2,017	2,310
Commercial bank debt, net of debt discount	7,743
Less interest and final payment	(901)
Commercial bank debt	$ 6,842

Debt, Commitments and Conting25

Debt, Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended				3 Months Ended		6 Months Ended
	May. 31, 2015	Jan. 31, 2015	Dec. 31, 2011	Oct. 31, 2007	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Debt Instrument [Line Items]
Noncancellable operating lease expiration period							2017-05
Extended term of lease			5 years
Rent expense					$ 100,000	$ 100,000	$ 200,000	$ 100,000
Convertible promissory note	$ 2,000,000						2,000,000
Accrued interest on convertible promissory note	$ 500,000
Research and development expenses					7,502,000	3,638,000	14,095,000	8,026,000
The Scripps Research Institute [Member] | Maximum [Member]
Debt Instrument [Line Items]
Obligation to pay an aggregate amount under agreement				$ 2,750,000
Research Funding and Option Agreement [Member] | The Scripps Research Institute [Member]
Debt Instrument [Line Items]
Agreement renewal period				12 months
Written notice period to terminate the agreement				30 days
Issue of common stock, shares in consideration for adjustment of sublicense payments		119,840
Fair value of common stock issued		$ 1,400,000
Research and development expenses					200,000	200,000	300,000	300,000
Research Funding and Option Agreement [Member] | National Foundation for Cancer Research [Member]
Debt Instrument [Line Items]
Charitable donations					$ 100,000	$ 100,000	$ 200,000	$ 200,000
Master Services Agreement [Member]
Debt Instrument [Line Items]
Milestones payment terms							Up to the total payment in the mid seven figures.
Subordinated Unsecured Convertible Promissory Note [Member]
Debt Instrument [Line Items]
Convertible promissory note borrowed			$ 2,000,000
Interest rate on convertible promissory note			8.00%
Convertible promissory note, description							The convertible promissory note carried an annual interest rate of 8.0% and matured at the earlier of (i) May 2015, (ii) a liquidation event, or (iii) the closing of an initial firm commitment underwritten public offering of the Company’s common stock pursuant to a registration statement under the Act, at which time all outstanding principal and accrued interest amounts would be due, unless previously converted.

Debt, Commitments and Conting26

Debt, Commitments and Contingencies - Schedule of Future Minimum Payments under Non-cancelable Operating Lease (Detail) $ in Thousands	Jun. 30, 2015USD ($)
Leases, Operating [Abstract]
2,015	$ 299
2,016	610
2,017	231
Operating Lease , total	$ 1,140

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Detail) - 6 months ended Jun. 30, 2015 - $ / shares	Total
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Options, Beginning Balance	1,514,471
Number of Options, Granted	1,050,045
Number of Options, Exercised	(166,454)
Number of Options, Canceled	(2,774)
Number of Options, Ending Balance	2,395,288
Weighted Average Price, Beginning Balance	$ 4.60
Weighted Average Price, Granted	11.35
Weighted Average Price, Exercised	2.87
Weighted Average Price, Canceled	4.25
Weighted Average Price, Ending Balance	$ 7.70

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Allocation of Stock-Based Compensation for All Options and Restricted Stock Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 816	$ 165	$ 1,419	$ 312
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	441	50	796	93
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 375	$ 115	$ 623	$ 219

Stockholders' Equity - Summar29

Stockholders' Equity - Summary of Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Employee Stock Option Grants (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate			2.14%
Expected volatility			111.10%
Expected dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 9 months 7 days	5 years 9 months 7 days	6 years 6 months 7 days
Risk-free interest rate	1.47%	1.47%
Expected volatility	81.60%	81.60%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 6 months 22 days
Risk-free interest rate	1.78%	1.78%
Expected volatility	88.10%	100.90%

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail)	May. 12, 2015USD ($)shares	Apr. 25, 2015shares	Mar. 31, 2015USD ($)$ / sharesshares	Jun. 30, 2015shares	Dec. 31, 2014shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				3,813,021	11,053,954
Convertible preferred stock, shares issued				0	73,487,415
2015 ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				227,623
IPO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of public offering | $	$ 86,300,000
IPO [Member] | 2015 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effective date of plan				May 6, 2015
Number of common stock shares reserved for issuance		1,574,566
Stock option grants description		The number of shares reserved and available for issuance under the 2015 Plan will automatically increase each January 1, beginning on January 1, 2016 and thereafter until January 1, 2019, by the lesser of (i) 1,840,000 shares, (ii) 4% of the outstanding number of shares of the Company's common stock on the immediately preceding December 31 or (iii) an amount determined by the Company's board of directors.
Percentage threshold of outstanding shares as of December 31 of each year for calculation of annual increase in authorized shares under the plan		4.00%
IPO [Member] | 2015 ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Effective date of plan				May 6, 2015
Number of common stock shares reserved for issuance		227,623
Percentage threshold of outstanding shares as of December 31 of each year for calculation of annual increase in authorized shares under the plan		1.00%
IPO [Member] | Maximum [Member] | 2015 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in shares authorized under plan, shares threshold		1,840,000
IPO [Member] | Series E redeemable convertible preferred stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Convertible preferred stock, shares issued			68,166,894
Convertible preferred stock, purchase price | $ / shares			$ 1.119
Convertible preferred stock, total cash consideration | $			$ 76,300,000
Convertible preferred stock, Issuance costs | $			$ 600,000
Conversion of convertible preferred stock to common stock			0.12572
Conversion of redeemable convertible preferred stock into common stock	7,040,991
IPO [Member] | Series E redeemable convertible preferred stock [Member] | Scenario Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Conversion of convertible preferred stock to common stock			0.10329
IPO [Member] | Series E redeemable convertible preferred stock [Member] | Minimum [Member] | Scenario Forecast [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of public offering | $			$ 50,000,000
Sale of stock, price per share | $ / shares			$ 13

Stockholders' Equity - Summar31

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Jun. 30, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	3,813,021	11,053,954
Redeemable Convertible Preferred Stock Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		9,238,868
Conversion of Redeemable Convertible Preferred Stock Issuable upon Conversion of Promissory Note [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		94,455
Redeemable Convertible Preferred Stock Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		25,970
Warrants for Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	25,970
2015 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	1,164,140	180,190
2015 ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	227,623
Common Stock Options Granted and Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	2,395,288	1,514,471