0001564590-21-028014 | 10-Q | XBRL Viewer

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License, Collaboration and Other Agreements - Additional Information (Detail) - USD ($)	1 Months Ended				3 Months Ended		12 Months Ended
	Jan. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jan. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payment received				$ 8,000,000
Milestone payments received	$ 2,000,000
Hong Kong University of Science and Technology [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaborative Agreement Funding Received			$ 750,000
Funding Of Project Cost Description			The grant will fund approximately 50% of the total estimated project cost, with aTyr contributing the remaining 50%. The research grant agreement between Pangu BioPharma, HKUST and the Government of the Hong Kong Special Administration Region became effective April 1, 2020
Expenses					$ 200,000	$ 0
Development Regulatory And Sales Milestones [Member] \| Kyorin Pharmaceutical Co Ltd [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Remaining receivable based on achievement of research milestones				165,000,000
Research Collaboration and Option Agreement [Member] \| Kyorin Pharmaceutical Co Ltd [Member] \| Collaboration Revenue [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payments received	$ 2,000,000
Stand-alone selling price of license		$ 100,000		$ 7,900,000
License and collaboration agreement revenue						8,000,000	$ 2,000,000
Research Collaboration and Option Agreement [Member] \| CSL Behring [Member] \| Collaboration Revenue [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payment received					$ 0	$ 7,900,000

Fair Value Measurements - Schedule of Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	$ 38,057	$ 14,730
Gross Unrealized Gains		7
Gross Unrealized Losses	(7)
Market Value	38,050	14,737
Short-term Investments [Member] \| Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	18,183	5,491
Gross Unrealized Gains		3
Market Value	18,183	5,494
Short-term Investments [Member] \| Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	1,008	2,218
Gross Unrealized Gains		1
Market Value	1,008	2,219
Short-term Investments [Member] \| Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Amortized Cost	18,866	7,021
Gross Unrealized Gains		3
Gross Unrealized Losses	(7)
Market Value	$ 18,859	$ 7,024

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2021

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	March 31, 2021
Common stock warrants		13,760
Common stock options and restricted stock units		898,306
Shares available under the 2015 equity incentive plan		63,391
Shares available under the employee stock purchase plan		75,315
		1,050,772

Summary of Stock Option Activity

The following table summarizes our stock option activity under all equity incentive plans for the three months ended March 31, 2021:


	Number of Outstanding Stock Options			Weighted Average Exercise Price
Outstanding as of December 31, 2020		576,534		$	23.33
Granted		326,456		$	4.52
Canceled/forfeited/expired		(12,184	)	$	25.47
Outstanding as of March 31, 2021		890,806		$	16.49

Schedule of Restricted Stock Unit Activity

The following table summarizes our restricted stock unit activity under all equity incentive plans for the three months ended March 31, 2021:

	Number of Outstanding Restricted Stock Units			Weighted Average Grant Date Fair Value
Balance as of December 31, 2020		7,677		$	5.32
Granted		4,000		$	3.89
Released		(4,177	)	$	6.18
Balance as of March 31, 2021		7,500		$	4.08

Schedule of Allocation of Stock-Based Compensation for All Options Including Performance Options with Market Condition, 2015 ESPP and Restricted Stock Units

The allocation of stock-based compensation for all options, 2015 Employee Stock Purchase Plan and restricted stock units is as follows (in thousands):

	March 31,
	2021		2020
Research and development	$	63	$	62
General and administrative		297		361
Total stock-based compensation expense	$	360	$	423

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:

	March 31,
	2021		2020
Expected term (in years)	5.99 – 6.02			6.02
Risk-free interest rate	0.6% – 0.9%			1.5	%
Expected volatility	104.0% – 104.8%			102.2	%
Expected dividend yield		0.0%		0.0	%

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

Schedule of Common Equivalent Shares Excluded for Calculation of Diluted Earning Per Share

For the three months ended March 31, 2021, common stock from the following would have had an anti-dilutive effect on net loss per share (in common share equivalents):

Common stock warrants			13,760
Common stock options and restricted stock units			898,306
Employee stock purchase plan			1,602
Total			913,668

For the three months ended March 31, 2020, the calculation excluded the following common equivalent shares because the effect on diluted earnings per share was anti-dilutive:

Common stock warrants			13,904
Common stock options and restricted stock units			486,142
Employee stock purchase plan			1,958
Total			502,004

Stockholders' Equity - Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants, Employee Stock Purchase Plan and Performance Options with Market Condition (Detail) - Employee Stock Option [Member]	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.60%	1.50%
Risk-free interest rate, maximum	0.90%
Expected volatility, minimum	104.00%	102.20%
Expected volatility, maximum	104.80%
Expected dividend yield	0.00%	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 11 months 26 days	6 years 7 days
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 7 days

Debt, Commitments and Contingencies

3 Months Ended

Mar. 31, 2021

Debt Instruments [Abstract]

Debt, Commitments and Contingencies

4. Debt, Commitments and Contingencies

Facility Leases

Future minimum payments under the non-cancelable facility lease and reconciliation to the operating lease liability as of March 31, 2021 were as follows (in thousands):

	Operating Lease
2021	$	776
2022		1,062
2023		404
Less: Amount representing interest		(207	)
Present value of lease payments		2,035
Less: Current portion of operating lease liability		(890	)
Long-term operating lease liability, net of current portion	$	1,145

For each of the three months ended March 31, 2021 and 2020, we recorded an operating lease expense of $0.2 million. As of March 31, 2021, the weighted-average remaining lease term was 2.2 years and the weighted-average discount rate was 9.6%.

Stockholders' Equity - Schedule of Allocation of Stock-Based Compensation for All Options 2015 ESPP and Restricted Stock Units (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 360	$ 423
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	63	62
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 297	$ 361

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail)	Mar. 31, 2021 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	1,050,772
Common Stock Warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	13,760
Common Stock Options and Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	898,306
Shares Available Under the 2015 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	63,391
Shares Available Under the 2015 ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	75,315

License, Collaboration and Other Agreements

3 Months Ended

Mar. 31, 2021

License Agreement [Abstract]

License Collaboration and Other Agreements

3. License, Collaboration and Other Agreements

Kyorin Pharmaceutical Co., Ltd.

In January 2020, we entered into a collaboration and license agreement with Kyorin Pharmaceutical Co., Ltd. (Kyorin) for the development and commercialization of ATYR1923 for interstitial lung diseases (ILD) in Japan. Under the agreement (the Kyorin Agreement), Kyorin received an exclusive right to develop and commercialize ATYR1923 in Japan for all forms of ILD. Under the terms of the Kyorin Agreement, Kyorin is obligated to fund all research, development, regulatory, marketing and commercialization activities in Japan. In September 2020, Kyorin began dosing patients in a Phase 1 clinical trial of ATYR1923 (known as KRP-R120 in Japan) and completed the last subject visit in December 2020. The Phase 1 clinical trial, which was conducted and funded by Kyorin, is a placebo-controlled study to evaluate the safety, pharmacokinetics and immunogenicity of ATYR1923. Results from this study are intended to enable Kyorin to initiate clinical trials in ILD in Japan. We received an $8.0 million upfront payment in January 2020 and a $2.0 milestone payment in January 2021 upon completion of enrollment in the Phase 1 clinical trial, and we are eligible to receive up to an additional $165.0 million in the aggregate upon achievement of certain development, regulatory and sales milestones, as well as tiered royalties ranging from the mid-single digits to mid-teens on net sales in Japan.

Following the first anniversary of the effective date of the Kyorin Agreement, Kyorin has the right to terminate the agreement for any reason upon 90 days advance written notice. Either party may terminate the Kyorin Agreement in the event that the other party breaches the agreement and fails to cure the breach, becomes insolvent or challenges certain of the intellectual property rights licensed under the agreement.

We assessed our license and collaboration with Kyorin in accordance with Topic 606 and concluded that Kyorin is a customer. We identified the following performance obligations under the Kyorin Agreement: 1) the license of ATYR1923 for ILD in Japan; and 2) free clinical trial material for Kyorin’s Phase 1 clinical trial. The $8.0 million upfront payment received from Kyorin is non-refundable and non-creditable and is considered fixed consideration. We determined that the relative stand-alone selling price was $7.9 million when the license was delivered to Kyorin in January 2020. We determined that the relative standalone selling price was $0.1 million for the free clinical trial material delivered to Kyorin in June 2020, using the “expected cost plus a margin” approach. In December 2020, Kyorin completed the last subject visit in its Phase 1 clinical trial of ATYR1923. This achievement triggered a $2.0 million milestone payment which we recognized as license and collaboration revenue in December 2020. We received the $2.0 million from Kyorin in January 2021.

For the three months ended March 31, 2021, there were no activities that triggered additional license and collaboration agreement revenue. For the three months ended March 31, 2020, we recognized $7.9 million as license and collaboration agreement revenue for the upfront payment received.

Both the milestones and royalty payments under the Kyorin Agreement are variable consideration. Since milestone payments are binary in nature, we will use the “most-likely” method to evaluate whether the milestones should be included as revenue. We will apply constraint to these amounts until the milestone is probable of being achieved. The royalties are dependent on future sales by Kyorin which are at the full discretion of Kyorin. Accordingly, we will apply a constraint to these amounts until the future sale sales have occurred.

Hong Kong University of Science and Technology

In March 2020, our subsidiary, Pangu BioPharma, together with the Hong Kong University of Science and Technology (HKUST) was awarded a grant of approximately $750,000 to build a high-throughput platform for the development of bi-specific antibodies. The two-year project is being funded by the Hong Kong Government’s Innovation and Technology Commission (ITC) under the Partnership Research Program (PRP). The PRP aims to support research and development projects undertaken by companies in collaboration with local universities and public research institutions. The grant will fund approximately 50% of the total estimated project cost, with aTyr contributing the remaining 50%. The research grant agreement between Pangu BioPharma, HKUST and the Government of the Hong Kong Special Administration Region became effective April 1, 2020.

Fair Value Measurements - Additional Information (Detail) - Position	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, investments in unrealized loss positions, number of positions		15
Available-for-sale, investments in unrealized loss positions, number of positions, less than twelve months		25
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments effective maturity period	2 years

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 12,587	$ 16,952
Available-for-sale investments	38,050	14,737
Other receivables	89	2,039
Prepaid expenses	1,408	1,803
Total current assets	52,134	35,531
Property and equipment, net	874	899
Right-of-use assets	1,886	2,083
Other assets	234	213
Total assets	55,128	38,726
Current liabilities:
Accounts payable	1,161	1,431
Accrued expenses	2,400	3,572
Current portion of operating lease liability	890	861
Total current liabilities	4,451	5,864
Long-term operating lease liability, net of current portion	1,145	1,378
Commitments and contingencies (Note 4)
Stockholders’ equity:
Preferred stock, $0.001 par value per share; 5,000,000 undesignated authorized shares; Class X Convertible Preferred Stock issued and outstanding shares – 0 as of March 31, 2021 (unaudited) and December 31, 2020, respectively
Common stock, $0.001 par value per share; 21,425,000 authorized shares as of March 31, 2021 and December 31, 2020, respectively; issued and outstanding shares – 16,011,385 (unaudited) and 11,018,954 as of March 31, 2021 and December 31, 2020, respectively	16	11
Additional paid-in capital	395,422	370,210
Accumulated other comprehensive loss	(57)	(43)
Accumulated deficit	(345,679)	(338,528)
Total aTyr Pharma stockholders’ equity	49,702	31,650
Noncontrolling interest in Pangu BioPharma Limited	(170)	(166)
Total stockholders' equity	49,532	31,484
Total liabilities and stockholders’ equity	$ 55,128	$ 38,726

Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 11,958	$ 13,708
Total assets measured at fair value	50,008	28,445
Available-for-sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	38,050	14,737
Available-for-sale [Member] \| Short-term Investments [Member] \| Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	1,008	2,219
Available-for-sale [Member] \| Short-term Investments [Member] \| Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	18,183	5,494
Available-for-sale [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	18,859	7,024
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	11,958	13,708
Total assets measured at fair value	11,958	13,708
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	38,050	14,737
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	38,050	14,737
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member] \| Short-term Investments [Member] \| Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	1,008	2,219
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [Member] \| Short-term Investments [Member] \| Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	18,183	5,494
Significant Other Observable Inputs (Level 2) [Member] \| Available-for-sale [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	$ 18,859	$ 7,024

Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Consolidated net income (loss)	$ (7,155)	$ 1,752
Other comprehensive loss:
Change in unrealized loss on available-for-sale investments, net of tax	(14)	(13)
Comprehensive income (loss)	(7,169)	1,739
Comprehensive loss attributable to noncontrolling interest Pangu BioPharma Limited	4	1
Comprehensive income (loss) attributable to aTyr Pharma, Inc. common stockholders	$ (7,165)	$ 1,740

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

+ References + Details

- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

+ References

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+ Details

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	21,425,000	21,425,000
Common stock, shares issued	16,011,385	11,018,954
Common stock, shares outstanding	16,011,385	11,018,954
Class X Convertible Preferred Stock [Member]
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2021	May 07, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Document Quarterly Report	true
Document Transition Report	false
Security Exchange Name	NASDAQ
Trading Symbol	LIFE
Entity Registrant Name	aTYR PHARMA INC
Entity Central Index Key	0001339970
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		16,064,643
Entity File Number	001-37378
Entity Tax Identification Number	20-3435077
Entity Address, Address Line One	3545 John Hopkins Court
Entity Address, Address Line Two	Suite #250
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Incorporation, State or Country Code	DE
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	731-8389
Title of 12(b) Security	Common Stock, par value $0.001 per share

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

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 development of innovative medicines based on novel biological pathways.

Principles of Consolidation

Our condensed 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 follow 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, 2020, contained in our Annual Report on Form 10-K filed with the SEC on March 24, 2021. 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.

Risks and Uncertainties

The impact of the COVID-19 pandemic has been and will likely continue to be extensive in many aspects of society, which has resulted in and will likely continue to result in significant disruptions to the global economy, as well as businesses and capital markets around the world. Impacts to our business have included the delay in enrollment of our Phase 1b/2a clinical trial in patients with pulmonary sarcoidosis and the discontinuation of some patients in that trial, temporary closures of portions of our facilities and those of our licensees and collaborators, disruptions or restrictions on our employee's ability to travel and delays in certain research and development activities. Other potential impacts to our business include, but are not limited to disruptions to or delays in other clinical trials, third-party manufacturing supply and other operations, inflation, the potential diversion of healthcare resources away from the conduct of clinical trials to focus on pandemic concerns, interruptions or delays in the operations of the FDA or other regulatory authorities, and our ability to raise capital and conduct business development activities.

Liquidity and Financial Condition

We have incurred net losses in each year since our inception in 2005, including a condensed consolidated net loss of $7.2 million for the three months ended March 31, 2021. As of March 31, 2021, we had an accumulated deficit of $345.7 million. We believe that our existing cash, cash equivalents and available-for-sale investments of $50.6 million as of March 31, 2021 will be sufficient to meet our anticipated cash requirements for a period of at least one year from the filing date of this Quarterly Report on Form 10-Q.

We do not expect to generate any revenues from product sales unless and until we successfully complete development and obtain regulatory approval for one or more of our product candidates, which we expect will take a number of years at a minimum. If we obtain regulatory approval for any of our product candidates, we expect to incur significant commercialization expenses related to product sales, marketing, manufacturing and distribution. Accordingly, we will need to raise substantial additional capital to fund our operations. The amount and timing of our future funding requirements will depend on many factors, including the pace and results of our preclinical and clinical development efforts and the timing and nature of the regulatory approval process for our product candidates. We anticipate that we will seek to fund our operations through equity offerings, grant funding, collaborations, strategic partnerships and/or licensing arrangements, and when we are closer to commercialization of our product candidates potentially through debt financings. However, we may be unable to raise additional capital or enter into such arrangements when needed on favorable terms or at all. Our failure to raise capital or enter into such arrangements when needed would have a negative impact on our financial condition and ability to develop our product candidates.

Use of Estimates

Our condensed consolidated financial statements are prepared in accordance with GAAP. The preparation of our condensed consolidated financial statements requires us to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure for these items in our condensed consolidated financial statements and accompanying notes. The most significant estimates in our condensed consolidated financial statements relate to the fair value of equity issuances and awards, clinical trial and research and development expenses. 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.

Reclassifications

Certain reclassifications have been made to prior year amounts to conform to the current year presentation. The reclassifications were not material to the condensed consolidated financial statements.

Leases

We follow Accounting Standards Codification (ASC) Topic 842, Leases in recording our operating and financing leases. For our long-term operating leases, we recognized a right-of-use asset and a lease liability in our condensed consolidated balance sheets. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that we would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. The right-of-use asset is based on the liability adjusted for any prepaid or deferred rent. We determine the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. We also made accounting policy elections not to apply the recognition requirements under Topic 842 to any of our short-term leases and to account for each separate lease and associated non-lease components as a single lease component for all of our leases. Under Topic 842 we determine if an arrangement is a lease at inception. Our right-of-use assets consist of an operating lease for our facility headquarters. We have a noncancelable operating lease that includes 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.

Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses in our condensed consolidated statements of operations.

Revenue Recognition

We evaluate our agreements under ASC Topic 606, Revenue from Contracts with Customers and ASC Topic 808, Collaborative Arrangements. We recognize revenue when we transfer promised goods or services to customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those goods or services. In determining the appropriate amount of revenue to be recognized as we fulfill our obligations under our agreement, we perform the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) we satisfy each performance obligation. As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. We use key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

We recognize revenue in one of two ways, over time or at a point in time. We recognize revenue over time when we are executing on our performance obligation over time and our partner receives benefit over time. For example, we recognize revenue over time when we provide research and development services. We recognize revenue at a point in time when we transfer control of a distinct performance obligation to our partner. For example, if a license to our intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license.

Basic and Diluted Net Income (Loss) Per Share

Basic net income (loss) per share is calculated by dividing the net income (loss) by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents.

Diluted Net Income (Loss) Per Share

For the three months ended March 31, 2021, common stock from the following would have had an anti-dilutive effect on net loss per share (in common share equivalents):

Common stock warrants			13,760
Common stock options and restricted stock units			898,306
Employee stock purchase plan			1,602
Total			913,668

For the three months ended March 31, 2020, we had net income available to common stockholders. As a result, we computed diluted net income per share using the weighted average number of common shares and dilutive common equivalent shares outstanding during the period. Dilutive common equivalent shares outstanding included 3,006 shares of restricted stock units.

For the three months ended March 31, 2020, the calculation excluded the following common equivalent shares because the effect on diluted earnings per share was anti-dilutive:

Common stock warrants			13,904
Common stock options and restricted stock units			486,142
Employee stock purchase plan			1,958
Total			502,004

Recent Accounting Pronouncements

In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses (Topic 326), to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, the amendments in Topic 326 replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Topic 326 is effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years for smaller reporting companies. We expect the adoption of the amendments in Topic 326 to not have a material effect in our condensed consolidated financial position or results of operations when such amendment is adopted.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740), Simplifying the Accounting for Income Taxes to identify, evaluate, and improve areas of GAAP for which costs and complexity can be reduced while maintaining or improving the usefulness of the information provided to users of financial statements. The amendments for Topic 740 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. Topic 740 is effective for fiscal years beginning after December 15, 2020 which we adopted on January 1, 2021. The adoption did not have an effect on our condensed consolidated financial position or results of operations.

Stockholders' Equity - Schedule of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member]	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Number of Outstanding Restricted Stock Units, Beginning Balance \| shares	7,677
Number of Outstanding Restricted Stock Units, Granted \| shares	4,000
Number of Outstanding Restricted Stock Units, Released \| shares	(4,177)
Number of Outstanding Restricted Stock Units, Ending Balance \| shares	7,500
Weighted Average Grant Date Fair Value, Beginning Balance \| $ / shares	$ 5.32
Weighted Average Grant Date Fair Value, Granted \| $ / shares	3.89
Weighted Average Grant Date Fair Value, Released \| $ / shares	6.18
Weighted Average Grant Date Fair Value, Ending Balance \| $ / shares	$ 4.08

Debt, Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2021

Debt Instruments [Abstract]

Schedule of Future Minimum Payments under Non-cancelable Operating Lease and Reconciliation to Operating Lease Liability

Future minimum payments under the non-cancelable facility lease and reconciliation to the operating lease liability as of March 31, 2021 were as follows (in thousands):

	Operating Lease
2021	$	776
2022		1,062
2023		404
Less: Amount representing interest		(207	)
Present value of lease payments		2,035
Less: Current portion of operating lease liability		(890	)
Long-term operating lease liability, net of current portion	$	1,145

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Sep. 30, 2020	Feb. 29, 2020	Mar. 31, 2021	Nov. 30, 2020	Mar. 10, 2020	May 31, 2019
Aspire Capital [Member]
Class Of Stock [Line Items]
Shares issued during the period			3,000,000
Shares issued, price per share			$ 5.09
Net proceeds from issuance of common stock			$ 15,200,000
Long-term purchase commitment, period	30 months
Long-term purchase commitment, description	upon the terms and subject to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $20.0 million of shares of our common stock at our request from time to time during the 30 month term of the Purchase Agreement.
Maximum [Member] \| Aspire Capital [Member]
Class Of Stock [Line Items]
Commitment to purchase shares	$ 20,000,000
A T M Offering Program \| Jones Trading Institutional Services L L C
Class Of Stock [Line Items]
Commission rate equal to gross proceeds			3.00%
A T M Offering Program \| Sale Agreement [Member] \| Maximum [Member] \| Jones Trading Institutional Services L L C
Class Of Stock [Line Items]
Agreed upon value of sale of common stock per transaction						$ 25,000,000
A T M Offering Program \| H.C. Wainwright & Co., LLC [Member]
Class Of Stock [Line Items]
Commission rate equal to gross proceeds						3.00%
Terminated value of sale of common stock			$ 20,000,000
Shares issued, price per share			$ 4.99
Net proceeds from issuance of common stock			$ 9,600,000
A T M Offering Program \| H.C. Wainwright & Co., LLC [Member] \| Sale Agreement [Member] \| Maximum [Member]
Class Of Stock [Line Items]
Agreed upon value of sale of common stock per transaction				$ 20,000,000		$ 10,000,000
A T M Offering Program \| Common Stock [Member] \| H.C. Wainwright & Co., LLC [Member]
Class Of Stock [Line Items]
Shares issued during the period			1,988,254
Public Offering [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of common stock		$ 20,700,000
Public Offering [Member] \| Common Stock [Member]
Class Of Stock [Line Items]
Shares issued during the period		4,235,294
Shares issued, price per share		$ 4.25
Issuance of additional share of common stock					635,294

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Common Equivalent Shares Excluded for Calculation of Diluted Earning Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not considered for calculation of diluted net loss per share	913,668	502,004
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not considered for calculation of diluted net loss per share	13,760	13,904
Common Stock Options and Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not considered for calculation of diluted net loss per share	898,306	486,142
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not considered for calculation of diluted net loss per share	1,602	1,958

Debt, Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Instruments [Abstract]
Operating lease, cost	$ 0.2	$ 0.2
Operating lease, weighted average remaining lease term	2 years 2 months 12 days
Operating lease, weighted average discount rate	9.60%

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Total revenues		$ 8,065
Operating expenses:
Research and development	$ 4,516	3,616
General and administrative	2,686	2,590
Total operating expenses	7,202	6,206
Income (loss) from operations	(7,202)	1,859
Total other income (expense), net	47	(107)
Consolidated net income (loss)	(7,155)	1,752
Net loss attributable to noncontrolling interest in Pangu BioPharma Limited	4	1
Net income (loss) attributable to aTyr Pharma, Inc.	$ (7,151)	$ 1,753
Basic, net income (loss) per share	$ (0.51)	$ 0.25
Shares used in computing basic net income (loss) per share	14,103,783	6,881,791
Diluted net income (loss) per share	$ (0.51)	$ 0.25
Shares used in computing diluted net income (loss) per share	14,103,783	6,884,797
License and Collaboration Agreement Revenues [Member]
Revenues:
Total revenues		$ 8,065

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Consolidated net income (loss)	$ (7,155)	$ 1,752
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	121	157
Stock-based compensation	360	423
Debt discount accretion and non-cash interest expense		129
Amortization (accretion) of premium (discount) of available-for-sale investment securities	51	(24)
Amortization of right-of-use assets	176	201
Loss on disposal of property and equipment		6
Changes in operating assets and liabilities:
Other receivables	1,950	48
Prepaid expenses and other assets	395	188
Accounts payable and accrued expenses	(1,521)	(578)
Contract liability		(65)
Operating lease liability	(204)	(179)
Net cash provided by (used in) operating activities	(5,827)	2,058
Cash flows from investing activities:
Purchases of property and equipment	(17)	(166)
Purchases of available-for-sale investment securities	(25,678)	(3,081)
Maturities of available-for-sale investment securities	2,300	14,650
Proceeds from sale of property and equipment		3
Net cash provided by (used in) investing activities	(23,395)	11,406
Cash flows from financing activities:
Proceeds from issuance of common stock from at the market offerings, net of offering costs	9,621
Proceeds from issuance of common stock from committed purchase agreement, net of offering costs	15,236
Proceeds from issuance of common stock from underwritten follow-on offering, net of offering costs		18,779
Repayments on borrowings		(2,000)
Net cash provided by financing activities	24,857	16,779
Net change in cash and cash equivalents	(4,365)	30,243
Cash and cash equivalents at beginning of period	16,952	9,210
Cash and cash equivalents at the end of period	$ 12,587	$ 39,453

Stockholders' Equity

3 Months Ended

Mar. 31, 2021

Equity [Abstract]

Stockholders' Equity

5. Stockholders’ Equity

At the Market Offering Program

In May 2019, we entered into a sales agreement with H.C. Wainwright & Co., LLC (Wainwright) with respect to an at-the-market offering (ATM Offering Program) under which we could offer and sell shares of our common stock having an aggregate offering price of up to $10.0 million. In November 2020, we amended our sales agreement with Wainwright to increase the amount of the ATM Offering Program up to $20.0 million. Wainwright was entitled to a commission at a fixed rate equal to 3% of the gross proceeds. In March 2021, the ATM Offering Program with Wainwright automatically terminated upon the issuance and sale of all of the shares of common stock having an aggregate offering price of $20.0 million. For the three months ended March 31, 2021, we sold an aggregate of 1,988,254 shares of common stock at an average price of $4.99 per share for net proceeds of $9.6 million under the ATM Offering Program.

In March 2021, we entered into a Capital on Demand^TM Sales Agreement with JonesTrading Institutional Services LLC (JonesTrading) for a new ATM Offering Program, pursuant to which we can sell from time to time, at our option, up to an aggregate of $25.0 million of shares of our common stock through JonesTrading, as sales agent or principal. JonesTrading is entitled to a commission at a fixed rate equal of up to 3% of the gross proceeds. For the three months ended March 31, 2021, we did not issue any shares under this ATM Offering Program.

Underwritten Follow-On Public Offering

In February 2020, we completed an underwritten follow-on public offering of 4,235,294 shares of our common stock at a price to the public of $4.25 per share. In March 2020, the underwriters fully exercised their option to purchase additional shares resulting in the issuance of an additional 635,294 shares of common stock. The total gross proceeds from the underwritten follow-on public offering, including the underwriters’ option to purchase additional shares, was approximately $20.7 million, before deducting underwriting discounts, commissions and offering expenses payable by us.

Purchase Agreement

In September 2020, we entered into a common stock purchase agreement (Purchase Agreement) with Aspire Capital Fund, LLC (Aspire Capital), which provides that, upon the terms and subject to the conditions and limitations set forth therein, Aspire Capital is committed to purchase up to an aggregate of $20.0 million of shares of our common stock at our request from time to time during the 30 month term of the Purchase Agreement. Concurrently with entering into the Purchase Agreement, we also entered into a registration rights agreement with Aspire Capital, in which we agreed to file one or more registration statements, as permissible and necessary to register under the Securities Act of 1933, as amended, for the resale of the shares of our common stock that have been and may be issued to Aspire Capital under the Purchase Agreement. For the three months ended March 31, 2021, we sold an aggregate of 3,000,000 shares of common stock at an average price of $5.09 per share for net proceeds of $15.2 million under this Purchase Agreement.

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	March 31, 2021
Common stock warrants		13,760
Common stock options and restricted stock units		898,306
Shares available under the 2015 equity incentive plan		63,391
Shares available under the employee stock purchase plan		75,315
		1,050,772

Equity Incentive Plans

The following table summarizes our stock option activity under all equity incentive plans for the three months ended March 31, 2021:


	Number of Outstanding Stock Options			Weighted Average Exercise Price
Outstanding as of December 31, 2020		576,534		$	23.33
Granted		326,456		$	4.52
Canceled/forfeited/expired		(12,184	)	$	25.47
Outstanding as of March 31, 2021		890,806		$	16.49

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:

	March 31,
	2021		2020
Expected term (in years)	5.99 – 6.02			6.02
Risk-free interest rate	0.6% – 0.9%			1.5	%
Expected volatility	104.0% – 104.8%			102.2	%
Expected dividend yield		0.0%		0.0	%

The following table summarizes our restricted stock unit activity under all equity incentive plans for the three months ended March 31, 2021:

	Number of Outstanding Restricted Stock Units			Weighted Average Grant Date Fair Value
Balance as of December 31, 2020		7,677		$	5.32
Granted		4,000		$	3.89
Released		(4,177	)	$	6.18
Balance as of March 31, 2021		7,500		$	4.08

Stock-based Compensation

The allocation of stock-based compensation for all options, 2015 Employee Stock Purchase Plan and restricted stock units is as follows (in thousands):

	March 31,
	2021		2020
Research and development	$	63	$	62
General and administrative		297		361
Total stock-based compensation expense	$	360	$	423

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2021

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

Principles of Consolidation

Unaudited Interim Financial Information

Risks and Uncertainties

Liquidity and Financial Condition

Use of Estimates

Reclassifications

Certain reclassifications have been made to prior year amounts to conform to the current year presentation. The reclassifications were not material to the condensed consolidated financial statements.

Leases

Rent expense for the operating lease is recognized on a straight-line basis over the lease term and is included in operating expenses in our condensed consolidated statements of operations.

Revenue Recognition

Basic and Diluted Net Income (Loss) Per Share

Diluted Net Income (Loss) Per Share

For the three months ended March 31, 2021, common stock from the following would have had an anti-dilutive effect on net loss per share (in common share equivalents):

Common stock warrants			13,760
Common stock options and restricted stock units			898,306
Employee stock purchase plan			1,602
Total			913,668

For the three months ended March 31, 2020, the calculation excluded the following common equivalent shares because the effect on diluted earnings per share was anti-dilutive:

Common stock warrants			13,904
Common stock options and restricted stock units			486,142
Employee stock purchase plan			1,958
Total			502,004

Recent Accounting Pronouncements

Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on Recurring Basis

Assets measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of March 31, 2021
Assets:
Current:
Cash equivalents	$	11,958	$	11,958	$	—	$	—
Available-for-sale investments:
Asset-backed securities		1,008		—		1,008		—
Commercial paper		18,183		—		18,183		—
Corporate debt securities		18,859		—		18,859		—
Total available-for-sale investments		38,050		—		38,050		—
Total assets measured at fair value	$	50,008	$	11,958	$	38,050	$	—

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2020
Assets:
Current:
Cash equivalents	$	13,708	$	13,708	$	—	$	—
Available-for-sale investments:
Asset-backed securities		2,219		—		2,219		—
Commercial paper		5,494		—		5,494		—
Corporate debt securities		7,024		—		7,024		—
Total available-for-sale investments		14,737		—		14,737		—
Total assets measured at fair value	$	28,445	$	13,708	$	14,737	$	—

Schedule of Available-for-sale Investments

As of March 31, 2021 and December 31, 2020, available-for-sale investments are detailed as follows (in thousands):

		March 31, 2021
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Market Value
Available-for-sale investments:
Asset-backed securities	Within 1 year	$	1,008	$	—	$	—		$	1,008
Commercial paper	Within 1 year		18,183		—		—			18,183
Corporate debt securities	1 to 2 years		18,866		—		(7	)		18,859
		$	38,057	$	—	$	(7	)	$	38,050

		December 31, 2020
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Market Value
Available-for-sale investments:
Asset-backed securities	Within 1 year	$	2,218	$	1	$	—	$	2,219
Commercial paper	Within 1 year		5,491		3		—		5,494
Corporate debt securities	Within 1 year		7,021		3		—		7,024
		$	14,730	$	7	$	—	$	14,737

Fair Value Measurements

3 Months Ended

Mar. 31, 2021

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. 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 commercial paper, corporate debt securities and asset-bask securities. We have no financial liabilities measured at fair value on a recurring basis. None of our non-financial assets and liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

Assets measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of March 31, 2021
Assets:
Current:
Cash equivalents	$	11,958	$	11,958	$	—	$	—
Available-for-sale investments:
Asset-backed securities		1,008		—		1,008		—
Commercial paper		18,183		—		18,183		—
Corporate debt securities		18,859		—		18,859		—
Total available-for-sale investments		38,050		—		38,050		—
Total assets measured at fair value	$	50,008	$	11,958	$	38,050	$	—

			Fair Value Measurements Using
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2020
Assets:
Current:
Cash equivalents	$	13,708	$	13,708	$	—	$	—
Available-for-sale investments:
Asset-backed securities		2,219		—		2,219		—
Commercial paper		5,494		—		5,494		—
Corporate debt securities		7,024		—		7,024		—
Total available-for-sale investments		14,737		—		14,737		—
Total assets measured at fair value	$	28,445	$	13,708	$	14,737	$	—

As of March 31, 2021 and December 31, 2020, available-for-sale investments are detailed as follows (in thousands):

		March 31, 2021
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Market Value
Available-for-sale investments:
Asset-backed securities	Within 1 year	$	1,008	$	—	$	—		$	1,008
Commercial paper	Within 1 year		18,183		—		—			18,183
Corporate debt securities	1 to 2 years		18,866		—		(7	)		18,859
		$	38,057	$	—	$	(7	)	$	38,050

		December 31, 2020
	Contractual Maturity	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Market Value
Available-for-sale investments:
Asset-backed securities	Within 1 year	$	2,218	$	1	$	—	$	2,219
Commercial paper	Within 1 year		5,491		3		—		5,494
Corporate debt securities	Within 1 year		7,021		3		—		7,024
		$	14,730	$	7	$	—	$	14,737

At each reporting date, we perform an evaluation of impairment to determine if any 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.

As of March 31, 2021, all of our available-for-sale investments had a variety of effective maturity dates of less than two years. As of March 31, 2021, 15 out of 25 of the available-for-sale investments were in gross unrealized loss positions.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock [Member]	Additional Paid-In Capital [Member]	Other Comprehensive Gain/(Loss) [Member]	Accumulated Deficit [Member]	Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2019	$ 21,026	$ 2	$ 4	$ 343,524	$ (40)	$ (322,304)	$ (160)
Begining balance, Shares at Dec. 31, 2019		1,643,961	3,891,787
Conversion of preferred stock to common stock		$ (2)	$ 1	1
Conversion of preferred stock to common stock, shares		(1,643,961)	587,444
Issuance of common stock upon release of restricted stock units			2,679
Issuance of common stock from underwritten follow-on offering, net of offering costs	18,779		$ 4	18,775
Issuance of common stock from underwritten follow-on offering, net of offering costs, shares			4,870,588
Stock-based compensation	423			423
Change in unrealized loss on available-for-sale investments, net of tax	(13)				(13)
Consolidated net income (loss)	1,752					1,753	(1)
Ending balance at Mar. 31, 2020	41,967		$ 9	362,723	(53)	(320,551)	(161)
Ending balance, Shares at Mar. 31, 2020			9,352,498
Beginning balance at Dec. 31, 2020	31,484		$ 11	370,210	(43)	(338,528)	(166)
Begining balance, Shares at Dec. 31, 2020			11,018,954
Issuance of common stock upon release of restricted stock units			4,177
Issuance of common stock from at the market offerings, net of offering costs	9,621		$ 2	9,619
Issuance of common stock from at the market offerings, net of offering costs, Shares			1,988,254
Issuance of common stock from committed purchase agreement, net of offering costs	15,236		$ 3	15,233
Issuance of common stock from committed purchase agreement, net of offering costs, shares			3,000,000
Stock-based compensation	360			360
Change in unrealized loss on available-for-sale investments, net of tax	(14)				(14)
Consolidated net income (loss)	(7,155)					(7,151)	(4)
Ending balance at Mar. 31, 2021	$ 49,532		$ 16	$ 395,422	$ (57)	$ (345,679)	$ (170)
Ending balance, Shares at Mar. 31, 2021			16,011,385

Stockholders' Equity - Summary of Stock Option Activity (Detail)	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Outstanding Stock Options, Beginning Balance \| shares	576,534
Number of Outstanding Stock Options, Granted \| shares	326,456
Number of Outstanding Stock Options, Canceled/forfeited/expired \| shares	(12,184)
Number of Outstanding Stock Options, Ending Balance \| shares	890,806
Weighted Average Exercise Price, Beginning Balance \| $ / shares	$ 23.33
Weighted Average Exercise Price, Granted \| $ / shares	4.52
Weighted Average Exercise Price, Canceled/forfeited/expired \| $ / shares	25.47
Weighted Average Exercise Price, Ending Balance \| $ / shares	$ 16.49

Debt, Commitments and Contingencies - Schedule of Future Minimum Payments under Non-cancelable Operating Lease and Reconciliation to Operating Lease Liability (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases Operating [Abstract]
2021	$ 776
2022	1,062
2023	404
Less: Amount representing interest	(207)
Present value of lease payments	2,035
Less: Current portion of operating lease liability	(890)	$ (861)
Long-term operating lease liability, net of current portion	$ 1,145	$ 1,378

Organization, Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Significant Accounting Policies [Line Items]
Net loss	$ (7,151)	$ 1,753
Accumulated deficit	345,679		$ 338,528
Cash, cash equivalents and available-for-sale investments	$ 50,600
Shares used in computing diluted net income (loss) per share	14,103,783	6,884,797
Restricted Stock Units [Member]
Significant Accounting Policies [Line Items]
Shares used in computing diluted net income (loss) per share		3,006
Pangu BioPharma [Member] \| Hong Kong [Member]
Significant Accounting Policies [Line Items]
Majority-owned subsidiary percentage	98.00%

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details