aTyr Pharma (ATYR) 10-Q 11 May 16 2016 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2016	May. 06, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
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		23,687,204

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 54,099	$ 53,025
Short-term investments	31,949	42,510
Prepaid expenses and other assets	1,575	2,415
Total current assets	87,623	97,950
Long-term investments	25,557	29,814
Property and equipment, net	1,845	1,793
Other assets	100	118
Total assets	115,125	129,675
Current liabilities:
Accounts payable	5,876	3,872
Accrued expenses	3,568	4,595
Current portion of deferred rent	320	315
Current portion of commercial bank debt	3,427	3,366
Total current liabilities	13,191	12,148
Deferred rent, net of current portion	49	130
Commercial bank debt, net of current portion	896	1,776
Other long-term liabilities	$ 557	$ 571
Commitments and contingencies (Note 3)
Redeemable convertible preferred stock, $0.001 par value; authorized shares – 7,285,456 at March 31, 2016 and December 31, 2015; issued and outstanding shares – none at March 31, 2016 and December 31, 2015
Stockholders’ equity:
Undesignated preferred stock, $0.001 par value; authorized shares – 5,000,000 at March 31, 2016 and December 31, 2015; issued and outstanding shares – none at March 31, 2016 and December 31, 2015
Common stock, $0.001 par value; authorized shares – 150,000,000 at March 31, 2016 and December 31, 2015; issued and outstanding shares – 23,677,303 at March 31, 2016 and 23,670,079 at December 31, 2015	$ 24	$ 24
Additional paid-in capital	274,638	273,321
Accumulated other comprehensive loss	(19)	(171)
Accumulated deficit	(174,211)	(158,124)
Total stockholders’ equity	100,432	115,050
Total liabilities, redeemable convertible preferred stock and stockholders’ equity	$ 115,125	$ 129,675

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2016	Dec. 31, 2015
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	23,677,303	23,670,079
Common stock, shares outstanding	23,677,303	23,670,079
Redeemable Convertible Preferred Stock [Member]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	7,285,456	7,285,456
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Undesignated Preferred Stock [Member]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating expenses:
Research and development	$ 12,000	$ 6,593
General and administrative	4,115	2,329
Total operating expenses	16,115	8,922
Loss from operations	(16,115)	(8,922)
Other income (expense), net	28	(149)
Net loss	$ (16,087)	$ (9,071)
Net loss per share, basic and diluted	$ (0.68)	$ (9.39)
Weighted average common stock shares outstanding, basic and diluted	23,631,133	966,322

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (16,087)	$ (9,071)
Other comprehensive income:
Unrealized gain on available-for-sale investments	152
Comprehensive loss	$ (15,935)	$ (9,071)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net loss	$ (16,087)	$ (9,071)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	233	209
Issuance of common stock for technology		1,411
Stock-based compensation	1,280	603
Amortization of debt discount	54	128
Change in fair value of preferred stock warrant liability		(77)
Amortization of investment premium	264	4
Deferred rent	(76)	(71)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	858	(187)
Accounts payable and accrued expenses	983	765
Net cash used in operating activities	(12,491)	(6,286)
Cash flows from investing activities:
Purchase of property and equipment	(314)	(123)
Purchases of investment securities	(9,994)
Maturities of investment securities	24,700	1,950
Net cash provided by investing activities	14,392	1,827
Cash flows from financing activities:
Issuance of preferred stock for cash, net of issuance costs		46,299
Proceeds from issuance of common stock through option exercises	11	69
Repayments on notes payable to bank	(838)	(795)
Costs paid in connection with initial public offering		(501)
Net cash (used in) provided by financing activities	(827)	45,072
Net change in cash and cash equivalents	1,074	40,613
Cash and cash equivalents at beginning of the period	53,025	13,899
Cash and cash equivalents at end of the period	$ 54,099	54,512
Supplemental schedule of noncash investing and financing activities:
Deferred initial public offering costs included in accounts payable and accrued expenses		$ 1,233

Organization, Business, Basis o

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2016
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. (we, us, and our) was incorporated in the state of Delaware on September 8, 2005. We are focused on the discovery and clinical development of innovative medicines for patients suffering from severe rare diseases. Initial Public Offering On May 12, 2015, we completed our 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). Principles of Consolidation Our consolidated financial statements include our accounts and our 98% majority-owned subsidiary in Hong Kong, Pangu BioPharma Limited (Pangu BioPharma). All intercompany transactions and balances are eliminated in consolidation. 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 our 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 our financial position and our results of operations and cash flows for periods presented. These statements do not include all disclosures required by GAAP and should be read in conjunction with our financial statements and accompanying notes for the fiscal year ended December 31, 2015, contained in our Annual Report on Form 10-K filed with the SEC on March 30, 2016. 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 Our consolidated financial statements are prepared in accordance with GAAP. The preparation of our consolidated financial statements requires us to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in our consolidated financial statements and accompanying notes. The most significant estimates in our 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 our knowledge of current events and actions we 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. We have excluded 44,136 and 39,439 shares subject to repurchase from the weighted average number of common shares outstanding for the three months ended March 31, 2016 and 2015, respectively. Diluted net loss per share is calculated by dividing the net loss 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 warrants for common stock and options outstanding under our 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 our 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 March 31, 2016 2015 Redeemable convertible preferred stock outstanding — 17,808,867 Redeemable convertible preferred stock issuable upon conversion of convertible promissory note — 94,455 Warrants for common stock 25,970 25,970 Common stock options and awards 3,742,770 1,799,392 Employee stock purchase plan 17,363 — 3,786,103 19,728,684 Recent Accounting Pronouncements In August 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-15, Presentation of Financial Statements — Going Concern. ASU 2014-15 provides that in connection with preparing financial statements for each annual and interim reporting period, an entity’s management should evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued (or within one year after the date that the financial statements are available to be issued when applicable). ASU 2014-15 is effective for the annual reporting period ending after December 15, 2016, and for annual and interim periods thereafter. Early adoption is permitted. The adoption of ASU 2014-15 is not expected to have a material impact on our consolidated financial position or results of operations. In April 2015, the FASB issued ASU No. 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from that debt liability, consistent with the presentation of a debt discount. The recognition and measurement guidance for debt issuance costs is not affected by ASU 2015-03. ASU 2015-03 is effective for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. We adopted ASU 2015-03 in January 2016 and the guidance did not affect our consolidated financial position or results of operations. In April 2015, the FASB issued ASU 2015-05, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement. ASU 2015-05 related to a customer’s accounting for fees in a cloud computing arrangement. This guidance requires that management evaluate each cloud computing arrangement in order to determine whether it includes a software license that must be accounted for separately from hosted services. We adopted ASU 2015-03 prospectively in January 2016 and the guidance did not have a material impact in our consolidated financial position or results of operations. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities, which requires that (i) all equity investments, other than equity-method investments, in unconsolidated entities generally be measured at fair value through earnings and (ii) when the fair value option has been elected for financial liabilities, changes in fair value due to instrument-specific credit risk will be recognized separately in other comprehensive income. Additionally, ASU 2016-01 changes the disclosure requirements for financial instruments. The new standard will be effective for fiscal years beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. Early adoption is permitted for certain provisions. The adoption of ASU 2015-03 is not expected to have a material impact on our consolidated financial position or results of operations. In February 2016, the FASB issued ASU 2016-02, Leases, to increase transparency and comparability among organizations by requiring recognition of lease assets and lease liabilities on the balance sheet and disclosure of key information about leasing arrangements. The new standard will become effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted, and is required to be adopted at the earliest period presented using a modified retrospective approach. We are currently evaluating the impact the provisions will have on our consolidated financial statements and whether we will adopt the guidance early. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation, which involves several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. ASU 2016-09 will be effective for the annual periods beginning after December 15, 2016 and interim periods within those annual periods, with early adoption permitted. We are currently evaluating the impact the provisions will have on our consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2016
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 us for loans with similar terms, which is considered a Level 2 input, we believe that the fair value of our commercial bank debt approximate their carrying values. Investment securities 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 we 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 our investments in corporate debt securities and commercial paper. We have no financial liabilities measured at fair value on a recurring basis. None of our 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 Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) As of March 31, 2016: Assets: Current: Cash equivalents $ 42,787 $ 42,787 $ — $ — Short-term investments: Commercial paper 1,998 — 1,998 — United States Treasury securities 3,003 3,003 — — Corporate debt securities 26,948 — 26,948 — Sub-total short-term investments 31,949 3,003 28,946 — Long-term investments: United States Treasury securities 5,003 5,003 — — Asset-backed securities 9,014 — 9,014 — Corporate debt securities 11,540 — 11,540 — Sub-total long-term investments 25,557 5,003 20,554 — Total assets measured at fair value $ 100,293 $ 50,793 $ 49,500 $ — As of December 31, 2015: Assets: Current: Cash equivalents $ 46,545 $ 46,545 $ — $ — Short-term investments: Commercial paper 2,996 — 2,996 — Corporate debt securities 39,514 — 39,514 — Sub-total short-term investments 42,510 — 42,510 — Long-term investments: United States Treasury securities 1,999 1,999 — — Asset-backed securities 10,912 — 10,912 — Corporate debt securities 16,903 — 16,903 — Sub-total long-term investments 29,814 1,999 27,815 — Total assets measured at fair value $ 118,869 $ 48,544 $ 70,325 $ — As of March 31, 2016 and December 31, 2015 available-for-sale investments are detailed as follows (in thousands): March 31, 2016 Gross Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Market Value Short-term investments: Commercial paper $ 1,998 $ — $ — $ 1,998 United States Treasury securities $ 3,002 $ 1 — $ 3,003 Corporate debt securities 26,964 5 (21 ) 26,948 $ 31,964 $ 6 $ (21 ) $ 31,949 Long-term investments: United States Treasury securities $ 4,999 $ 4 $ — $ 5,003 Asset-backed securities 9,010 5 (1 ) 9,014 Corporate debt securities 11,552 4 (16 ) 11,540 $ 25,561 $ 13 $ (17 ) $ 25,557 December 31, 2015 Gross Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Market Value Short-term investments: Commercial paper $ 2,996 $ — $ — $ 2,996 Corporate debt securities 39,575 — (61 ) 39,514 $ 42,571 $ — $ (61 ) $ 42,510 Long-term investments: United States Treasury securities $ 2,006 $ — $ (7 ) $ 1,999 Asset-backed securities 10,928 — (16 ) 10,912 Corporate debt securities 16,990 — (87 ) 16,903 $ 29,924 $ — $ (110 ) $ 29,814 Available-for-sale investments that are in an unrealized loss position as of March 31, 2016 are as follows (in thousands): Estimated Value Gross Unrealized Losses Asset-backed securities $ 2,000 $ (1 ) Corporate debt securities 19,079 (37 ) $ 21,079 $ (38 ) As of March 31, 2016, all available-for-sale investments have contractual maturity dates within two years. As of March 31, 2016, there are 12 available-for-sale investments in gross unrealized loss position, all of which had been in such position for less than twelve months. At each reporting date, we perform 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 our intent and ability to hold the investment until recovery of its amortized cost basis. We intend, and have the ability, to hold our investments in unrealized loss positions until their amortized cost basis has been recovered. Based on our evaluation, we determined that the unrealized losses were not other-than-temporary at March 31, 2016.

Debt, Commitments and Contingen

Debt, Commitments and Contingencies	3 Months Ended
	Mar. 31, 2016
Debt Instruments [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): March 31, 2016 December 31, 2015 Commercial bank debt $ 4,364 $ 5,202 Less debt discount, net of current portion (1 ) (6 ) Commercial bank debt, net of debt discount 4,363 5,196 Less current portion of commercial bank debt (3,467 ) (3,420 ) Commercial bank debt, net of current portion $ 896 $ 1,776 Current portion of commercial bank debt $ 3,467 $ 3,420 Current portion of debt discount (40 ) (54 ) Current portion of commercial bank debt, net of debt discount $ 3,427 $ 3,366 Future minimum principal and interest payments under our loan and security agreement with Silicon Valley Bank, including the final payment, are as follows (in thousands): March 31, 2016 2016 $ 2,716 2017 2,310 5,026 Less interest and final payment (662 ) Commercial bank debt $ 4,364 Facility Lease In December 2011, we 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 we have an option to extend the lease for a period of five years. Rent expense for the three months ended March 31, 2016 and 2015 was $0.1 million. In conjunction with this lease, we borrowed $2.0 million under a subordinated unsecured convertible promissory note issued to the venture arm of our 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 our 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 our IPO. Future minimum payments under the non-cancelable operating lease as of March 31, 2016 were as follows (in thousands): Operating Lease 2016 $ 461 2017 231 Total $ 692 Research Agreements and Funding Obligations In October 2007, we entered into a research funding and option agreement for certain technologies from The Scripps Research Institute (TSRI). Under the agreement, we provide 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 we provide 30 days’ prior written notice to terminate the agreement. TSRI has the right to terminate the agreement if we fail to make any payment under the agreement or for breach or insolvency. Under the research funding and option agreement, TSRI has granted us 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 we may receive from our sublicensees or partners, with the amount owed decreasing if we enter into the applicable sublicense or partnering agreement after meeting a specified clinical milestone. In addition, we are 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, we and TSRI entered into an amended and restated research funding and option agreement pursuant to which we agreed to issue 119,840 shares of our common stock to TSRI in consideration for the adjustment of sublicense payments and the assignment of certain intellectual property rights by TSRI to us. The $1.4 million fair value of the common stock issued to TSRI was recorded to research and development expense. We issued the shares of common stock to TSRI on March 31, 2015. During the three months ended March 31, 2016 and 2015, excluding the fair value of the common stock issued to TSRI described above, we recognized expense under the agreement in the amount of $0.4 million and $0.2 million, respectively. A member of our 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 March 31, 2016 and 2015, we provided charitable donations to the National Foundation for Cancer Research of $0.1 million. We have 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 our board of directors. FUJIFILM Diosynth Biotechnologies U.S.A., Inc. Agreement In June 2015, we 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 drug substance for Resolaris, our drug in clinical development. Pursuant to the MSA, Fujifilm will provide the drug substance 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 drug substance of Resolaris, and we are required to pay Fujifilm based on development and production milestones up to the total payment in the mid seven figures. In addition, we are billed for consumables on a pass-through basis. During the three months ended March 31, 2016 and 2015, expenses associated with this agreement were $1.6 million and $0.3 million, respectively.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2016
Equity [Abstract]
Stockholders' Equity	4. Stockholders’ Equity Stock Option and Incentive Plans 2014 Stock Plan We adopted a stock option plan in 2007 (the 2007 Plan), which was subsequently amended, restated and renamed in July 2014 (the 2014 Plan) to provide for the incentive stock options, nonstatutory stock options, stock and rights to purchase restricted stock to eligible recipients. Recipients of incentive stock options are eligible to purchase shares of our common stock at an exercise price equal to no less than the estimated fair market value of such stock on the date of grant. The maximum term of options under the 2014 Plan is ten years. Options granted generally vest over four years. 2015 Stock Plan In April 2015, our board of directors adopted, and our stockholders approved, the 2015 Plan. The 2015 Plan became effective on May 6, 2015 and we ceased granting any new awards under our 2014 Plan. Awards granted under the 2014 Plan prior to our 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. A total of 1,574,566 shares of our 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 our common stock on the immediately preceding December 31 or (iii) an amount determined by our board of directors. Shares underlying any awards under the 2015 Plan 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. Employee Stock Purchase Plan In April 2015, our board of directors adopted, and our stockholders approved, our 2015 Employee Stock Purchase Plan (the 2015 ESPP). The 2015 ESPP became effective on May 6, 2015. A total of 227,623 shares of our 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 our common stock on the immediately preceding December 31 or such lesser number of shares as determined by the administrator of the 2015 ESPP. Stock option activity is summarized as follows: Number of Outstanding Options Weighted Average Price Balance as of December 31, 2015 2,625,280 $ 8.83 Granted 1,310,569 $ 7.21 Exercised (5,144 ) $ 2.06 Canceled (314,448 ) $ 11.28 Balance as of March 31, 2016 3,616,257 $ 8.04 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 March 31, 2016 2015 Expected term (in years) 5.77 – 6.08 6.02 – 6.08 Risk-free interest rate 1.43% – 1.90 % 1.53 % Expected volatility 81.15% – 82.11 % 100.90 % Expected dividend yield 0.00 % 0.00 % In January 2016, we granted to our executives, employees and certain consultants performance options with a market condition to purchase up to an aggregate 396,960 shares of common stock at an exercise price of $9.13. Upon achievement of specified goals by January 4, 2018, such performance options shall begin to vest over four years in equal monthly installments, otherwise the options will be subject to forfeiture. The fair value of the stock options awarded that include market-based performance conditions is estimated on the date of the grant using a Monte Carlo simulation, based on the market price of the underlying common stock, expected performance measurement period, expected peer group stock price volatility and expected risk-free interest rate. The weighted average grant date fair value was $1.93. The performance options with market conditions grants are expensed using the accelerated attribution method over the requisite service period of 5.06 years regardless of whether the market condition is achieved or earned and vest. The assumptions used to determine the fair value of the performance options with a market condition were as follows: March 31, 2016 Expected term (in years) 5.06 Risk-free interest rate 2.24 % Expected volatility 83.26 % Expected dividend yield 0.0 % During the quarter ended March 31, 2016, we granted restricted stock units to employees. Restricted stock unit activity is summarized as follows: Number of Outstanding Restricted Stock Units Weighted Average Grant Date Fair Value Balance as of December 31, 2015 — $ — Granted 128,593 $ 5.00 Released (2,080 ) $ 5.48 Canceled — $ — Balance as of March 31, 2016 126,513 $ 4.99 The allocation of stock-based compensation for all options, including performance options with a market condition, and restricted stock units is as follows (in thousands): Three Months Ended March 31, 2016 2015 Research and development $ 547 $ 355 General and administrative 733 248 $ 1,280 $ 603 Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows: March 31, 2016 December 31, 2015 Common stock warrants 25,970 25,970 Common stock options and awards outstanding 3,742,770 2,625,280 Shares available under the 2014 Plan 984,357 984,357 Shares available under the 2015 Plan 1,709,796 903,350 Shares available under the 2015 ESPP Plan 464,323 227,623 6,927,216 4,766,580

Organization, Business, Basis11

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Organization and Business	Organization and Business aTyr Pharma, Inc. (we, us, and our) was incorporated in the state of Delaware on September 8, 2005. We are 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, we completed our 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).
Principles of Consolidation	Principles of Consolidation Our consolidated financial statements include our accounts and our 98% majority-owned subsidiary in Hong Kong, Pangu BioPharma Limited (Pangu BioPharma). All intercompany transactions and balances are eliminated in consolidation.
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 our 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 our financial position and our results of operations and cash flows for periods presented. These statements do not include all disclosures required by GAAP and should be read in conjunction with our financial statements and accompanying notes for the fiscal year ended December 31, 2015, contained in our Annual Report on Form 10-K filed with the SEC on March 30, 2016. 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 Our consolidated financial statements are prepared in accordance with GAAP. The preparation of our consolidated financial statements requires us to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in our consolidated financial statements and accompanying notes. The most significant estimates in our 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 our knowledge of current events and actions we 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. We have excluded 44,136 and 39,439 shares subject to repurchase from the weighted average number of common shares outstanding for the three months ended March 31, 2016 and 2015, respectively. Diluted net loss per share is calculated by dividing the net loss 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 warrants for common stock and options outstanding under our 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 our 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 March 31, 2016 2015 Redeemable convertible preferred stock outstanding — 17,808,867 Redeemable convertible preferred stock issuable upon conversion of convertible promissory note — 94,455 Warrants for common stock 25,970 25,970 Common stock options and awards 3,742,770 1,799,392 Employee stock purchase plan 17,363 — 3,786,103 19,728,684
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-15, Presentation of Financial Statements — Going Concern. ASU 2014-15 provides that in connection with preparing financial statements for each annual and interim reporting period, an entity’s management should evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued (or within one year after the date that the financial statements are available to be issued when applicable). ASU 2014-15 is effective for the annual reporting period ending after December 15, 2016, and for annual and interim periods thereafter. Early adoption is permitted. The adoption of ASU 2014-15 is not expected to have a material impact on our consolidated financial position or results of operations. In April 2015, the FASB issued ASU No. 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from that debt liability, consistent with the presentation of a debt discount. The recognition and measurement guidance for debt issuance costs is not affected by ASU 2015-03. ASU 2015-03 is effective for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. We adopted ASU 2015-03 in January 2016 and the guidance did not affect our consolidated financial position or results of operations. In April 2015, the FASB issued ASU 2015-05, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement. ASU 2015-05 related to a customer’s accounting for fees in a cloud computing arrangement. This guidance requires that management evaluate each cloud computing arrangement in order to determine whether it includes a software license that must be accounted for separately from hosted services. We adopted ASU 2015-03 prospectively in January 2016 and the guidance did not have a material impact in our consolidated financial position or results of operations. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities, which requires that (i) all equity investments, other than equity-method investments, in unconsolidated entities generally be measured at fair value through earnings and (ii) when the fair value option has been elected for financial liabilities, changes in fair value due to instrument-specific credit risk will be recognized separately in other comprehensive income. Additionally, ASU 2016-01 changes the disclosure requirements for financial instruments. The new standard will be effective for fiscal years beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. Early adoption is permitted for certain provisions. The adoption of ASU 2015-03 is not expected to have a material impact on our consolidated financial position or results of operations. In February 2016, the FASB issued ASU 2016-02, Leases, to increase transparency and comparability among organizations by requiring recognition of lease assets and lease liabilities on the balance sheet and disclosure of key information about leasing arrangements. The new standard will become effective for interim and annual periods beginning after December 15, 2018, with early adoption permitted, and is required to be adopted at the earliest period presented using a modified retrospective approach. We are currently evaluating the impact the provisions will have on our consolidated financial statements and whether we will adopt the guidance early. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation, which involves several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. ASU 2016-09 will be effective for the annual periods beginning after December 15, 2016 and interim periods within those annual periods, with early adoption permitted. We are currently evaluating the impact the provisions will have on our consolidated financial statements.

Organization, Business, Basis12

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2016
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 March 31, 2016 2015 Redeemable convertible preferred stock outstanding — 17,808,867 Redeemable convertible preferred stock issuable upon conversion of convertible promissory note — 94,455 Warrants for common stock 25,970 25,970 Common stock options and awards 3,742,770 1,799,392 Employee stock purchase plan 17,363 — 3,786,103 19,728,684

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2016
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 Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) As of March 31, 2016: Assets: Current: Cash equivalents $ 42,787 $ 42,787 $ — $ — Short-term investments: Commercial paper 1,998 — 1,998 — United States Treasury securities 3,003 3,003 — — Corporate debt securities 26,948 — 26,948 — Sub-total short-term investments 31,949 3,003 28,946 — Long-term investments: United States Treasury securities 5,003 5,003 — — Asset-backed securities 9,014 — 9,014 — Corporate debt securities 11,540 — 11,540 — Sub-total long-term investments 25,557 5,003 20,554 — Total assets measured at fair value $ 100,293 $ 50,793 $ 49,500 $ — As of December 31, 2015: Assets: Current: Cash equivalents $ 46,545 $ 46,545 $ — $ — Short-term investments: Commercial paper 2,996 — 2,996 — Corporate debt securities 39,514 — 39,514 — Sub-total short-term investments 42,510 — 42,510 — Long-term investments: United States Treasury securities 1,999 1,999 — — Asset-backed securities 10,912 — 10,912 — Corporate debt securities 16,903 — 16,903 — Sub-total long-term investments 29,814 1,999 27,815 — Total assets measured at fair value $ 118,869 $ 48,544 $ 70,325 $ —
Schedule of Available-for-sale Investments	As of March 31, 2016 and December 31, 2015 available-for-sale investments are detailed as follows (in thousands): March 31, 2016 Gross Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Market Value Short-term investments: Commercial paper $ 1,998 $ — $ — $ 1,998 United States Treasury securities $ 3,002 $ 1 — $ 3,003 Corporate debt securities 26,964 5 (21 ) 26,948 $ 31,964 $ 6 $ (21 ) $ 31,949 Long-term investments: United States Treasury securities $ 4,999 $ 4 $ — $ 5,003 Asset-backed securities 9,010 5 (1 ) 9,014 Corporate debt securities 11,552 4 (16 ) 11,540 $ 25,561 $ 13 $ (17 ) $ 25,557 December 31, 2015 Gross Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Market Value Short-term investments: Commercial paper $ 2,996 $ — $ — $ 2,996 Corporate debt securities 39,575 — (61 ) 39,514 $ 42,571 $ — $ (61 ) $ 42,510 Long-term investments: United States Treasury securities $ 2,006 $ — $ (7 ) $ 1,999 Asset-backed securities 10,928 — (16 ) 10,912 Corporate debt securities 16,990 — (87 ) 16,903 $ 29,924 $ — $ (110 ) $ 29,814
Schedule of Available-for-sale Investments in Unrealized Loss Position	Available-for-sale investments that are in an unrealized loss position as of March 31, 2016 are as follows (in thousands): Estimated Value Gross Unrealized Losses Asset-backed securities $ 2,000 $ (1 ) Corporate debt securities 19,079 (37 ) $ 21,079 $ (38 )

Debt, Commitments and Conting14

Debt, Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2016
Debt Instruments [Abstract]
Schedule of Commercial Bank Debt and Unamortized Discount	Commercial bank debt and unamortized discount balances are as follows (in thousands): March 31, 2016 December 31, 2015 Commercial bank debt $ 4,364 $ 5,202 Less debt discount, net of current portion (1 ) (6 ) Commercial bank debt, net of debt discount 4,363 5,196 Less current portion of commercial bank debt (3,467 ) (3,420 ) Commercial bank debt, net of current portion $ 896 $ 1,776 Current portion of commercial bank debt $ 3,467 $ 3,420 Current portion of debt discount (40 ) (54 ) Current portion of commercial bank debt, net of debt discount $ 3,427 $ 3,366
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 our loan and security agreement with Silicon Valley Bank, including the final payment, are as follows (in thousands): March 31, 2016 2016 $ 2,716 2017 2,310 5,026 Less interest and final payment (662 ) Commercial bank debt $ 4,364
Schedule of Future Minimum Payments under Non-cancelable Operating Lease	Future minimum payments under the non-cancelable operating lease as of March 31, 2016 were as follows (in thousands): Operating Lease 2016 $ 461 2017 231 Total $ 692

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2016
Summary of Stock Option Activity	Stock option activity is summarized as follows: Number of Outstanding Options Weighted Average Price Balance as of December 31, 2015 2,625,280 $ 8.83 Granted 1,310,569 $ 7.21 Exercised (5,144 ) $ 2.06 Canceled (314,448 ) $ 11.28 Balance as of March 31, 2016 3,616,257 $ 8.04
Schedule of Restricted Stock Units Activity	During the quarter ended March 31, 2016, we granted restricted stock units to employees. Restricted stock unit activity is summarized as follows: Number of Outstanding Restricted Stock Units Weighted Average Grant Date Fair Value Balance as of December 31, 2015 — $ — Granted 128,593 $ 5.00 Released (2,080 ) $ 5.48 Canceled — $ — Balance as of March 31, 2016 126,513 $ 4.99
Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition and Restricted Stock Units	The allocation of stock-based compensation for all options, including performance options with a market condition, and restricted stock units is as follows (in thousands): Three Months Ended March 31, 2016 2015 Research and development $ 547 $ 355 General and administrative 733 248 $ 1,280 $ 603
Summary of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows: March 31, 2016 December 31, 2015 Common stock warrants 25,970 25,970 Common stock options and awards outstanding 3,742,770 2,625,280 Shares available under the 2014 Plan 984,357 984,357 Shares available under the 2015 Plan 1,709,796 903,350 Shares available under the 2015 ESPP Plan 464,323 227,623 6,927,216 4,766,580
Employee Stock Option [Member]
Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition	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 March 31, 2016 2015 Expected term (in years) 5.77 – 6.08 6.02 – 6.08 Risk-free interest rate 1.43% – 1.90 % 1.53 % Expected volatility 81.15% – 82.11 % 100.90 % Expected dividend yield 0.00 % 0.00 %
Performance Options with Market Condition [Member]
Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition	The assumptions used to determine the fair value of the performance options with a market condition were as follows: March 31, 2016 Expected term (in years) 5.06 Risk-free interest rate 2.24 % Expected volatility 83.26 % Expected dividend yield 0.0 %

Organization, Business, Basis16

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	May. 12, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Initial public offering of common stock price per share		$ 0.001		$ 0.001
Weighted average shares subject to repurchase		44,136	39,439
Pangu BioPharma [Member] | Hong Kong [Member]
Significant Accounting Policies [Line Items]
Majority-owned subsidiary percentage		98.00%
IPO [Member]
Significant Accounting Policies [Line Items]
Issuance of common stock through initial public offering, net, Shares	6,164,000
Initial public offering of common stock price per share	$ 14
Gross proceeds	$ 86.3
Net proceeds	75.9
Underwriting and other expenses	10.4
Underwriting discounts and commissions	6
Other offering expenses	$ 4.4

Organization, Business, Basis17

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in calculation of diluted net loss per share	3,786,103	19,728,684
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		17,808,867
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
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 and Awards [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	3,742,770	1,799,392
Employee Stock Purchase Plan [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	17,363

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	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 42,787	$ 46,545
Total assets measured at fair value	100,293	118,869
Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	31,949	42,510
Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	1,998	2,996
Short-term Investments [Member] | United States Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	3,003
Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	26,948	39,514
Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	25,557	29,814
Long-term Investments [Member] | United States Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	5,003	1,999
Long-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	11,540	16,903
Long-term Investments [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	9,014	10,912
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 equivalents	42,787	46,545
Total assets measured at fair value	50,793	48,544
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	3,003
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-term Investments [Member] | United States Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	3,003
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	5,003	1,999
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Long-term Investments [Member] | United States Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	5,003	1,999
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	49,500	70,325
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	28,946	42,510
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	1,998	2,996
Significant Other Observable Inputs (Level 2) [Member] | Short-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	26,948	39,514
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	20,554	27,815
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	11,540	16,903
Significant Other Observable Inputs (Level 2) [Member] | Long-term Investments [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	$ 9,014	$ 10,912

Fair Value Measurements - Sch19

Fair Value Measurements - Schedule of Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	$ 31,964	$ 42,571
Gross Unrealized Gains	6
Gross Unrealized Losses	(21)	(61)
Market Value	31,949	42,510
Short-term Investments [Member] | United States Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	3,002
Gross Unrealized Gains	1
Market Value	3,003
Short-term Investments [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	26,964	39,575
Gross Unrealized Gains	5
Gross Unrealized Losses	(21)	(61)
Market Value	26,948	39,514
Short-term Investments [Member] | Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	1,998	2,996
Market Value	1,998	2,996
Long-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	25,561	29,924
Gross Unrealized Gains	13
Gross Unrealized Losses	(17)	(110)
Market Value	25,557	29,814
Long-term Investments [Member] | United States Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	4,999	2,006
Gross Unrealized Gains	4
Gross Unrealized Losses		(7)
Market Value	5,003	1,999
Long-term Investments [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	11,552	16,990
Gross Unrealized Gains	4
Gross Unrealized Losses	(16)	(87)
Market Value	11,540	16,903
Long-term Investments [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	9,010	10,928
Gross Unrealized Gains	5
Gross Unrealized Losses	(1)	(16)
Market Value	$ 9,014	$ 10,912

Fair Value Measurements - Sch20

Fair Value Measurements - Schedule of Available-for-sale Investments in Unrealized Loss Position (Detail) $ in Thousands	Mar. 31, 2016USD ($)
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 21,079
Gross Unrealized Losses	(38)
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2,000
Gross Unrealized Losses	(1)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	19,079
Gross Unrealized Losses	$ (37)

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2016Security
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Available-for-sale investments contractual maturity period	2 years
Available-for-sale investments in gross unrealized loss position	12
Available-for-sale investments in gross unrealized loss position	12 months

Debt, Commitments and Conting22

Debt, Commitments and Contingencies - Schedule of Commercial Bank Debt and Unamortized Discount (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Commercial bank debt, net of current portion	$ 896	$ 1,776
Current portion of commercial bank debt, net of debt discount	3,427	3,366
Commercial Bank Debt [Member]
Debt Instrument [Line Items]
Commercial bank debt	4,364	5,202
Less debt discount, net of current portion	(1)	(6)
Commercial bank debt, net of debt discount	4,363	5,196
Less current portion of commercial bank debt	(3,467)	(3,420)
Commercial bank debt, net of current portion	896	1,776
Current portion of commercial bank debt	3,467	3,420
Current portion of debt discount	(40)	(54)
Current portion of commercial bank debt, net of debt discount	$ 3,427	$ 3,366

Debt, Commitments and Conting23

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	Mar. 31, 2016USD ($)
Debt Instrument [Line Items]
2,016	$ 2,716
2,017	2,310
Commercial bank debt, net of debt discount	5,026
Less interest and final payment	(662)
Commercial bank debt	$ 4,364

Debt, Commitments and Conting24

Debt, Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended				3 Months Ended
	May. 31, 2015	Jan. 31, 2015	Dec. 31, 2011	Oct. 31, 2007	Mar. 31, 2016	Mar. 31, 2015
Debt Instrument [Line Items]
Noncancelable operating lease expiration period					2017-05
Extended term of lease			5 years
Rent expense					$ 100,000	$ 100,000
Convertible promissory note	$ 2,000,000
Accrued interest on convertible promissory note	$ 500,000
Research and development expenses					12,000,000	6,593,000
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					400,000	200,000
Research Funding and Option Agreement [Member] | National Foundation for Cancer Research [Member]
Debt Instrument [Line Items]
Charitable donations					100,000	100,000
Master Services Agreement [Member]
Debt Instrument [Line Items]
Research and development expenses					$ 1,600,000	$ 300,000
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
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 our 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 instrument interest rate percentage			8.00%

Debt, Commitments and Conting25

Debt, Commitments and Contingencies - Schedule of Future Minimum Payments under Non-cancelable Operating Lease (Detail) $ in Thousands	Mar. 31, 2016USD ($)
Leases Operating [Abstract]
2,016	$ 461
2,017	231
Total	$ 692

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - $ / shares	1 Months Ended		3 Months Ended
	Jan. 31, 2016	Apr. 30, 2015	Mar. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance			6,927,216	4,766,580
Outstanding stock options granted			1,310,569
Weighted average exercise price, granted			$ 7.21
Common Stock [Member] | Executives, Employees and Consultants [Member] | Performance Options with Market Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period	4 years
Outstanding stock options granted	396,960
Weighted average exercise price, granted	$ 9.13
Achievement of specified performance goals	Jan. 4, 2018
Weighted average grant date fair value of options granted	$ 1.93
Requisite service period	5 years 22 days
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term for stock option plan grant			10 years
Options vesting period			4 years
Number of common stock shares reserved for issuance			984,357	984,357
2015 Stock Option and Incentive Plan [Member] | IPO [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 our common stock on the immediately preceding December 31 or (iii) an amount determined by our 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%
2015 Stock Option and Incentive Plan [Member] | IPO [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in shares authorized under plan, shares threshold		1,840,000
2015 ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance			464,323	227,623
2015 ESPP Plan [Member] | IPO [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%

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2016$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Outstanding Options, Beginning Balance | shares	2,625,280
Number of Outstanding Options, Granted | shares	1,310,569
Number of Outstanding Options, Exercised | shares	(5,144)
Number of Outstanding Options, Canceled | shares	(314,448)
Number of Outstanding Options, Ending Balance | shares	3,616,257
Weighted Average Price, Beginning Balance | $ / shares	$ 8.83
Weighted Average Price, Granted | $ / shares	7.21
Weighted Average Price, Exercised | $ / shares	2.06
Weighted Average Price, Canceled | $ / shares	11.28
Weighted Average Price, Ending Balance | $ / shares	$ 8.04

Stockholders' Equity - Summar28

Stockholders' Equity - Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition (Detail)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2014
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		1.53%
Risk-free interest rate, minimum	1.43%
Risk-free interest rate, maximum	1.90%
Expected volatility		100.90%
Expected volatility, minimum	81.15%
Expected volatility, maximum	82.11%
Expected dividend yield	0.00%	0.00%	0.00%
Employee Stock Option [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 9 months 7 days	6 years 7 days
Employee Stock Option [Member] | 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
Performance Options with Market Condition [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 22 days
Risk-free interest rate	2.24%
Expected volatility	83.26%
Expected dividend yield	0.00%

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Restricted Stock Unit Activity (Detail) - Restricted Stock Unit [Member]	3 Months Ended
	Mar. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of Outstanding Restricted Stock Units, Granted | shares	128,593
Number of Outstanding Restricted Stock Units, Released | shares	(2,080)
Number of Outstanding Restricted Stock Units, Ending Balance | shares	126,513
Weighted Average Grant Date Fair Value, Granted | $ / shares	$ 5
Weighted Average Grant Date Fair Value, Released | $ / shares	5.48
Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 4.99

Stockholders' Equity - Schedu30

Stockholders' Equity - Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition and Restricted Stock Units (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,280	$ 603
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	547	355
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 733	$ 248

Stockholders' Equity - Summar31

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Mar. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	6,927,216	4,766,580
Common Stock Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	25,970	25,970
Shares Available Under the 2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	984,357	984,357
Shares Available Under the 2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	1,709,796	903,350
Shares Available Under the 2015 ESPP Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	464,323	227,623
Common Stock Options and Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	3,742,770	2,625,280