Kura Oncology (KURA) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 01, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	KURA
Entity Registrant Name	KURA ONCOLOGY, INC.
Entity Central Index Key	0001422143
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		66,555,775
Entity File Number	001-37620
Entity Tax Identification Number	61-1547851
Entity Address, Address Line One	12730 High Bluff Drive
Entity Address, Address Line Two	Suite 400
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92130
City Area Code	858
Local Phone Number	500-8800
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Balance Sheets (Unaud

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 39,183	$ 325,493
Short-term investments	504,262	307,827
Prepaid expenses and other current assets	5,460	3,972
Total current assets	548,905	637,292
Property and equipment, net	2,731	2,021
Restricted cash	210	210
Operating lease right-of-use assets	5,989	6,334
Other long-term assets	3,306	1,355
Total assets	561,141	647,212
Current liabilities:
Accounts payable and accrued expenses	21,926	23,024
Current portion of long-term debt		3,000
Total current liabilities	21,926	26,024
Long-term debt		4,250
Long-term operating lease liabilities	5,103	5,638
Other long-term liabilities	356	395
Total liabilities	27,385	36,307
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000 shares authorized; 66,504 and 66,194 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	7	7
Additional paid-in capital	934,168	913,354
Accumulated other comprehensive income (loss)	(194)	46
Accumulated deficit	(400,225)	(302,502)
Total stockholders' equity	533,756	610,905
Total liabilities and stockholders' equity	$ 561,141	$ 647,212

Condensed Balance Sheets (Una_2

Condensed Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	66,504,000	66,194,000
Common stock, shares outstanding	66,504,000	66,194,000

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Expenses:
Research and development	$ 22,367	$ 16,601	$ 63,765	$ 42,873
General and administrative	11,310	7,593	34,455	22,694
Total operating expenses	33,677	24,194	98,220	65,567
Other Income (Expense):
Interest and other income, net	311	571	911	2,535
Interest expense		(146)	(414)	(434)
Total other income (expense)	311	425	497	2,101
Net Loss	$ (33,366)	$ (23,769)	$ (97,723)	$ (63,466)
Net loss per share, basic and diluted	$ (0.50)	$ (0.42)	$ (1.47)	$ (1.24)
Weighted average number of shares used in computing net loss per share, basic and diluted	66,353	56,405	66,285	51,169
Comprehensive Loss:
Net loss	$ (33,366)	$ (23,769)	$ (97,723)	$ (63,466)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities and foreign currency	199	(333)	(240)	(107)
Comprehensive Loss	$ (33,167)	$ (24,102)	$ (97,963)	$ (63,573)

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid- In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 218,781	$ 5	$ 431,322	$ 331	$ (212,877)
Beginning balance (in shares) at Dec. 31, 2019		45,384
Issuance of common stock, net of offering costs	134,924	$ 1	134,923
Issuance of common stock, net of offering costs, (in shares)		10,465
Share-based compensation expense	9,065		9,065
Issuance of common stock from exercises of options and employee stock purchase plan	7,298		7,298
Issuance of common stock from exercises of options and employee stock purchase plan (in shares)		778
Other comprehensive income (loss)	(107)			(107)
Net loss	(63,466)				(63,466)
Ending balance at Sep. 30, 2020	306,495	$ 6	582,608	224	(276,343)
Ending balance (in shares) at Sep. 30, 2020		56,627
Beginning balance at Jun. 30, 2020	322,374	$ 6	574,385	557	(252,574)
Beginning balance (in shares) at Jun. 30, 2020		56,214
Share-based compensation expense	3,360		3,360
Issuance of common stock from exercise of options	4,863		4,863
Issuance of common stock from exercise of options (in shares)		413
Other comprehensive income (loss)	(333)			(333)
Net loss	(23,769)				(23,769)
Ending balance at Sep. 30, 2020	306,495	$ 6	582,608	224	(276,343)
Ending balance (in shares) at Sep. 30, 2020		56,627
Beginning balance at Dec. 31, 2020	610,905	$ 7	913,354	46	(302,502)
Beginning balance (in shares) at Dec. 31, 2020		66,194
Share-based compensation expense	17,182		17,182
Issuance of common stock from exercises of options and employee stock purchase plan	3,632		3,632
Issuance of common stock from exercises of options and employee stock purchase plan (in shares)		310
Other comprehensive income (loss)	(240)			(240)
Net loss	(97,723)				(97,723)
Ending balance at Sep. 30, 2021	533,756	$ 7	934,168	(194)	(400,225)
Ending balance (in shares) at Sep. 30, 2021		66,504
Beginning balance at Jun. 30, 2021	558,551	$ 7	925,796	(393)	(366,859)
Beginning balance (in shares) at Jun. 30, 2021		66,296
Share-based compensation expense	6,114		6,114
Issuance of common stock from exercise of options	2,258		2,258
Issuance of common stock from exercise of options (in shares)		208
Other comprehensive income (loss)	199			199
Net loss	(33,366)				(33,366)
Ending balance at Sep. 30, 2021	$ 533,756	$ 7	$ 934,168	$ (194)	$ (400,225)
Ending balance (in shares) at Sep. 30, 2021		66,504

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Net loss	$ (97,723)	$ (63,466)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	17,182	9,065
Non-cash interest expense	399
Loss on extinguishment of debt	212
Depreciation expense	392	86
Amortization of premium and accretion of discounts on marketable securities, net	3,175	42
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,488)	(237)
Other long-term assets	(746)	832
Accounts payable and accrued expenses	(2,549)	1,993
Other long-term liabilities	(39)	163
Net cash used in operating activities	(81,185)	(51,522)
Investing Activities
Purchases of marketable securities	(429,320)	(192,943)
Maturities of marketable securities	229,469	155,093
Purchases of property and equipment	(1,045)	(1,896)
Net cash used in investing activities	(200,896)	(39,746)
Financing Activities
Repayment of long-term debt	(7,250)
Payment of fees related to extinguishment of debt	(611)
Proceeds from exercises of stock options and purchases under employee stock purchase plan	3,632	7,298
Proceeds from issuance of common stock, net		135,000
Net cash (used in) provided by financing activities	(4,229)	142,298
Net (decrease) increase in cash, cash equivalents and restricted cash	(286,310)	51,030
Cash, cash equivalents and restricted cash at beginning of period	325,703	26,135
Cash, cash equivalents and restricted cash at end of period	$ 39,393	$ 77,165

Organization and Basis of Prese

Organization and Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation The Company Kura Oncology, Inc. is a clinical-stage biopharmaceutical company committed to realizing the promise of precision medicines for the treatment of cancer. Our pipeline consists of small molecule product candidates that target cancer signaling pathways where there is a strong scientific and clinical rationale to improve outcomes, and we intend to pair them with molecular or cellular diagnostics to identify those patients most likely to respond to treatment. We plan to advance our product candidates through a combination of internal development and strategic partnerships while maintaining significant development and commercial rights. References in these Notes to Unaudited Condensed Financial Statements to the “Company,” “we,” “our” or “us,” refer to Kura Oncology, Inc. Basis of Presentation The accompanying unaudited condensed financial statements should be read in conjunction with the audited financial statements and notes thereto in our Annual Report on Form 10-K for the fiscal year ended December 31, 2020, as filed with the Securities and Exchange Commission on February 24, 2021, from which we derived our balance sheet as of December 31, 2020. The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying unaudited condensed financial statements do not include all of the information and notes required by GAAP for complete financial statements. The accompanying unaudited condensed financial statements reflect all adjustments, consisting of normal recurring adjustments, that are, in the opinion of our management, necessary to a fair statement of the results for the interim periods presented. Interim results are not necessarily indicative of results for a full year. The preparation of the unaudited condensed financial statements in accordance with GAAP requires our management to make estimates and assumptions that affect the amounts reported on our unaudited condensed financial statements and accompanying notes. The amounts reported could differ under different estimates and assumptions. On an ongoing basis, we evaluate our estimates and judgments, which are based on historical and anticipated results and trends and on various other assumptions that management believes to be reasonable under the circumstances. Though the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty, we continue to use the best information available to inform our critical accounting estimates. By their nature, estimates are subject to an inherent degree of uncertainty and, as such, actual results may differ from management’s estimates. The extent to which the COVID-19 pandemic has impacted and may continue to impact our business will depend on future developments, which are highly uncertain and cannot be predicted with any confidence, such as the duration and severity of the COVID-19 pandemic, steps required or mandated by governments to mitigate the impact of COVID-19 or the effectiveness of actions to prevent, contain and treat COVID-19, particularly in the geographies where we, our third party manufacturers, contract research organizations or current and planned clinical trial sites operate. We cannot presently predict the scope and severity of any potential business disruptions, interruptions or shutdowns. If we or any of the third parties with whom we engage, however, were to experience shutdowns or other business disruptions, our ability to conduct our business in the manner and on the timelines presently planned could be materially and negatively affected, which could have a material adverse impact on our business and our results of operations and financial condition.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Reclassifications Certain prior period balances have been reclassified to conform to the current period presentation. Restricted Cash Under the terms of an office lease entered into in March 2020, we are required to maintain a standby letter of credit during the term of the lease. As of September 30, 2021, restricted cash of $0.2 million was pledged as collateral for the letter of credit. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the unaudited condensed balance sheets that sum to the total of the amounts shown in the unaudited condensed statements of cash flows, in thousands: September 30, 2021 December 31, 2020 September 30, 2020 December 31, 2019 Cash and cash equivalents $ 39,183 $ 325,493 $ 76,955 $ 26,135 Restricted cash 210 210 210 — Total $ 39,393 $ 325,703 $ 77,165 $ 26,135 Allowance for Credit Losses For available-for-sale debt securities in an unrealized loss position, we first assess whether we intend to sell, or it is more likely than not that we will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale debt securities that do not meet the aforementioned criteria, we evaluate whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, we consider the severity of the impairment, any changes in interest rates, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the unaudited condensed statements of operations and comprehensive loss. Concentration of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash, cash equivalents and short-term investments. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have established guidelines to limit our exposure to credit risk by placing investments with high credit quality financial institutions, diversifying our investment portfolio and placing investments with maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity. Net Loss per Share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common shares and common stock equivalents outstanding for the period determined using the treasury-stock method. Common stock equivalents outstanding are comprised of stock options, restricted stock units, a warrant and employee stock purchase plan rights and are only included in the calculation of diluted earnings per common share when net income is reported and their effect is dilutive. Because of our net loss for the three and nine months ended September 30, 2021 and 2020 , Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board or other standard setting bodies that we adopt as of the specified effective date. We have evaluated recently issued accounting pronouncements and , based on our preliminary assessment, we do not believe any will have a material impact on our unaudited con dens ed financial statements or related footnote disclosures.

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Investments All Other Investments [Abstract]
Investments	3. Investments We invest in available-for-sale securities consisting of money market funds, corporate debt securities, U.S. Treasury securities, commercial paper, non-U.S. government debt securities, supranational debt securities and U.S. Agency bonds. Available-for-sale securities are classified as part of either cash and cash equivalents or short-term investments on our unaudited condensed balance sheets. The following tables summarize, by major security type, our short-term investments that are measured at fair value on a recurring basis, in thousands: September 30, 2021 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 32,228 $ — $ — $ 32,228 Short-term investments: Corporate debt securities 3 or less 199,250 40 (126 ) 199,164 U.S. Treasury securities 3 or less 143,635 38 (92 ) 143,581 Commercial paper 1 or less 129,418 — — 129,418 Non-U.S. government and supranational debt securities 3 or less 23,151 — (30 ) 23,121 U.S. Agency bonds 2 or less 8,993 — (15 ) 8,978 Total short-term investments 504,447 78 (263 ) 504,262 Total $ 536,675 $ 78 $ (263 ) $ 536,490 December 31, 2020 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 311,239 $ — $ — $ 311,239 Commercial paper 1 or less 5,998 — — 5,998 Total cash equivalents 317,237 — — 317,237 Short-term investments: Corporate debt securities 2 or less 113,020 36 (36 ) 113,020 U.S. Treasury securities 1 or less 88,409 50 (2 ) 88,457 Commercial paper 1 or less 106,350 — — 106,350 Total short-term investments 307,779 86 (38 ) 307,827 Total $ 625,016 $ 86 $ (38 ) $ 625,064 Short-term investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. As of September 30, 2021 and December 31, 2020, short-term investments of $320.9 million and $242.6 million, respectively, had maturities less than one year, and short-term investments of $183.4 million and $65.2 million, respectively, had maturities between one to three years. We had no realized gains or losses for the three and nine months ended September 30, 2021. As of September 30, 2021, 22 available-for-sale debt securities with a fair market value of $200.2 million losses is the result of a credit loss. As such, we have no allowance for credit losses as of September 30, 2021 and December 31, 2020 . Unrealized gains and losses that are not credit-related are included in accumulated other comprehensive income (loss).

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements As of September 30, 2021 and December 31, 2020, we had cash equivalents and short-term investments measured at fair value on a recurring basis. Available-for-sale marketable securities consisted of U.S. Treasury securities, which are measured at fair value using Level 1 inputs, and corporate debt securities, commercial paper, non-U.S. government debt securities, supranational debt securities and U.S. Agency bonds, which are measured at fair value using Level 2 inputs. We determine the fair value of Level 2 related securities with the aid of valuations provided by third parties using proprietary valuation models and analytical tools. These valuation models and analytical tools use market pricing or prices for similar instruments that are both objective and publicly available, including matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids and/or offers. We validate the fair values of Level 2 financial instruments by comparing these fair values to a third-party pricing source. The following tables summarize, by major security type, our cash equivalents and short-term investments that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy, in thousands: September 30, 2021 Total Level 1 Level 2 Cash equivalents: Money market funds $ 32,228 $ 32,228 $ — Short-term investments: Corporate debt securities 199,164 — 199,164 U.S. Treasury securities 143,581 143,581 — Commercial paper 129,418 — 129,418 Non-U.S. government and supranational debt securities 23,121 — 23,121 U.S. Agency bonds 8,978 — 8,978 Total short-term investments 504,262 143,581 360,681 Total $ 536,490 $ 175,809 $ 360,681 December 31, 2020 Total Level 1 Level 2 Cash equivalents: Money market funds $ 311,239 $ 311,239 $ — Commercial paper 5,998 — 5,998 Total cash equivalents 317,237 311,239 5,998 Short-term investments: Corporate debt securities 113,020 — 113,020 U.S. Treasury securities 88,457 88,457 — Commercial paper 106,350 — 106,350 Total short-term investments 307,827 88,457 219,370 Total $ 625,064 $ 399,696 $ 225,368

Balance Sheet Detail

Balance Sheet Detail	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Detail	5. Balance Sheet Detail Property and equipment consisted of the following, in thousands: September 30, 2021 December 31, 2020 Leasehold improvements $ 1,532 $ 1,169 Furniture and fixtures 1,016 862 Laboratory and computer equipment 861 276 Property and equipment, gross 3,409 2,307 Less: accumulated depreciation (678 ) (286 ) Property and equipment, net $ 2,731 $ 2,021 Accounts payable and accrued expenses consisted of the following, in thousands: September 30, 2021 December 31, 2020 Accounts payable $ 2,875 $ 2,753 Accrued clinical trial research and development expenses 1,923 4,080 Accrued other research and development expenses 7,158 5,581 Accrued compensation and benefits 6,436 7,016 Operating lease liability, current portion 2,250 2,089 Other accrued expenses 1,284 1,505 Total accounts payable and accrued expenses $ 21,926 $ 23,024

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Long-Term Debt	6. Long-Term Debt In November 2018, we entered into a loan and security agreement with Silicon Valley Bank, or the SVB Loan Agreement, providing for up to $20.0 million in a series of term loans. Upon entering into the SVB Loan Agreement, we borrowed $7.5 million, or the Term Loan. The Term Loan had a scheduled maturity date of . Debt Modifications and Extinguishments

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	7. Leases In January 2020, we entered into an office lease agreement for our corporate offices in San Diego, California. This agreement was originally scheduled to commence in May 2020 unaudited condensed In March 2020, we entered into a lease agreement for office space in Boston, Massachusetts, or the Boston Lease, which commenced on April 1, 2020 and expires on July 31, 2024. The Boston Lease provides for a one-time option to extend the Boston Lease for a period of five additional years after the expiration of the initial lease term. Under the terms of the Boston Lease, monthly base rent was approximately $105,500 for the first year, subject to an annual fixed percentage increase of 2.0% on April 1 st of each year . In addition, we are obligated to pay for common area maintenance and other costs. Under the terms of the Boston Lease , we are required to maintain a standby letter of credit of approximately $ 0.2 million during the term of the lease. We recorded an operating lease ROU asset and operating lease liability of approximately $ 5.1 million on our unaudited condensed balance sheet on the lease commencement date during the quarter ended June 30, 2020 . In May 2020, we entered into a two-year unaudited condensed In May 2021, we entered into an operating lease agreement for lab and office space in San Diego, California, or the Morehouse Lease, which commenced on August 10, 2021 and expires on August 31, 2025. Under the terms of the Morehouse Lease, the monthly base rent is approximately $24,000 for the first year, subject to an annual fixed percentage increase of 3% each year. The Morehouse Lease provided approximately $106,000 in reimbursements for allowable tenant improvements, which effectively reduced the total lease payments owed for the Morehouse Lease. We are obligated to pay for common area maintenance and other costs associated with the Morehouse Lease. For accounting purposes, the lease commencement date was determined to be July 2021 when we had control of the lab and office space. We recorded an operating lease ROU asset and operating lease liability of approximately $1.0 million on our unaudited condensed Maturities of lease liabilities as of September 30, 2021 are as follows, in thousands: Year Ending December 31, 2021 (remaining) $ 572 2022 2,319 2023 2,375 2024 1,863 2025 929 Total lease payments 8,058 Less: imputed interest (705 ) Total operating lease liabilities $ 7,353 As of September 30, 2021 and December 31, 2020, total operating lease ROU assets were $6.0 million and $6.3 million, respectively. As of September 30, 2021, total operating lease liabilities were $7.4 million, of which $5.1 million were recorded as long-term lease liabilities. As of December 31, 2020, total operating lease liabilities were $7.7 million, of which $5.6 million were recorded as long-term lease liabilities. As of September 30, 2021 and December 31, 2020, the weighted-average discount rate was 5.5%, and the weighted-average remaining lease term was 3.5 years and 4.1 years, respectively. Total cash paid for amounts included in the measurement of operating lease liabilities, net of tenant improvement reimbursements, was $1.5 million and $0.1 million for the nine months ended September 30, 2021 Total operating lease expense $0.5 entered into short-term operating leases which expired in 2020 that are not recorded on the unaudited condensed balance sheet s . Total rent expense for the three months ended September 30, 2021 and 2020 was approximately $ million in both periods . Total rent expense for the nine months ended September 30, 2021 and 2020 was approximately $ 1.5 million and $ 1.4 million, respectively .

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	8. Share-Based Compensation The following table summarizes share-based compensation expense for all share-based compensation arrangements, in thousands: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Research and development $ 2,059 $ 1,003 $ 5,277 $ 2,618 General and administrative 4,055 2,357 11,905 6,447 Total share-based compensation expense $ 6,114 $ 3,360 $ 17,182 $ 9,065 During 2021, we began issuing restricted stock units, or RSUs. As of September 30, 2021, unrecognized estimated compensation expense related to stock options and RSUs was approximately $55.0 million and $4.4 million, respectively, which is expected to be recognized over a weighted average period of approximately 2.6 years and 3.3 years, respectively.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Reclassifications	Reclassifications Certain prior period balances have been reclassified to conform to the current period presentation.
Restricted Cash	Restricted Cash Under the terms of an office lease entered into in March 2020, we are required to maintain a standby letter of credit during the term of the lease. As of September 30, 2021, restricted cash of $0.2 million was pledged as collateral for the letter of credit. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the unaudited condensed balance sheets that sum to the total of the amounts shown in the unaudited condensed statements of cash flows, in thousands: September 30, 2021 December 31, 2020 September 30, 2020 December 31, 2019 Cash and cash equivalents $ 39,183 $ 325,493 $ 76,955 $ 26,135 Restricted cash 210 210 210 — Total $ 39,393 $ 325,703 $ 77,165 $ 26,135
Allowance for Credit Losses on Available-for-Sale Debt Securities	Allowance for Credit Losses For available-for-sale debt securities in an unrealized loss position, we first assess whether we intend to sell, or it is more likely than not that we will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale debt securities that do not meet the aforementioned criteria, we evaluate whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, we consider the severity of the impairment, any changes in interest rates, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the unaudited condensed statements of operations and comprehensive loss.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash, cash equivalents and short-term investments. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have established guidelines to limit our exposure to credit risk by placing investments with high credit quality financial institutions, diversifying our investment portfolio and placing investments with maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.
Net Loss per Share	Net Loss per Share Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common shares and common stock equivalents outstanding for the period determined using the treasury-stock method. Common stock equivalents outstanding are comprised of stock options, restricted stock units, a warrant and employee stock purchase plan rights and are only included in the calculation of diluted earnings per common share when net income is reported and their effect is dilutive. Because of our net loss for the three and nine months ended September 30, 2021 and 2020 ,
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board or other standard setting bodies that we adopt as of the specified effective date. We have evaluated recently issued accounting pronouncements and , based on our preliminary assessment, we do not believe any will have a material impact on our unaudited con dens ed financial statements or related footnote disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the unaudited condensed balance sheets that sum to the total of the amounts shown in the unaudited condensed statements of cash flows, in thousands: September 30, 2021 December 31, 2020 September 30, 2020 December 31, 2019 Cash and cash equivalents $ 39,183 $ 325,493 $ 76,955 $ 26,135 Restricted cash 210 210 210 — Total $ 39,393 $ 325,703 $ 77,165 $ 26,135

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Investments All Other Investments [Abstract]
Investments Measured at Fair Value on Recurring Basis	The following tables summarize, by major security type, our short-term investments that are measured at fair value on a recurring basis, in thousands: September 30, 2021 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 32,228 $ — $ — $ 32,228 Short-term investments: Corporate debt securities 3 or less 199,250 40 (126 ) 199,164 U.S. Treasury securities 3 or less 143,635 38 (92 ) 143,581 Commercial paper 1 or less 129,418 — — 129,418 Non-U.S. government and supranational debt securities 3 or less 23,151 — (30 ) 23,121 U.S. Agency bonds 2 or less 8,993 — (15 ) 8,978 Total short-term investments 504,447 78 (263 ) 504,262 Total $ 536,675 $ 78 $ (263 ) $ 536,490 December 31, 2020 Maturities (years) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds 1 or less $ 311,239 $ — $ — $ 311,239 Commercial paper 1 or less 5,998 — — 5,998 Total cash equivalents 317,237 — — 317,237 Short-term investments: Corporate debt securities 2 or less 113,020 36 (36 ) 113,020 U.S. Treasury securities 1 or less 88,409 50 (2 ) 88,457 Commercial paper 1 or less 106,350 — — 106,350 Total short-term investments 307,779 86 (38 ) 307,827 Total $ 625,016 $ 86 $ (38 ) $ 625,064

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule Of Fair Value Measurements, By Major Security Type	The following tables summarize, by major security type, our cash equivalents and short-term investments that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy, in thousands: September 30, 2021 Total Level 1 Level 2 Cash equivalents: Money market funds $ 32,228 $ 32,228 $ — Short-term investments: Corporate debt securities 199,164 — 199,164 U.S. Treasury securities 143,581 143,581 — Commercial paper 129,418 — 129,418 Non-U.S. government and supranational debt securities 23,121 — 23,121 U.S. Agency bonds 8,978 — 8,978 Total short-term investments 504,262 143,581 360,681 Total $ 536,490 $ 175,809 $ 360,681 December 31, 2020 Total Level 1 Level 2 Cash equivalents: Money market funds $ 311,239 $ 311,239 $ — Commercial paper 5,998 — 5,998 Total cash equivalents 317,237 311,239 5,998 Short-term investments: Corporate debt securities 113,020 — 113,020 U.S. Treasury securities 88,457 88,457 — Commercial paper 106,350 — 106,350 Total short-term investments 307,827 88,457 219,370 Total $ 625,064 $ 399,696 $ 225,368

Balance Sheet Detail (Tables)

Balance Sheet Detail (Tables)	9 Months Ended
	Sep. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment	Property and equipment consisted of the following, in thousands: September 30, 2021 December 31, 2020 Leasehold improvements $ 1,532 $ 1,169 Furniture and fixtures 1,016 862 Laboratory and computer equipment 861 276 Property and equipment, gross 3,409 2,307 Less: accumulated depreciation (678 ) (286 ) Property and equipment, net $ 2,731 $ 2,021
Summary of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consisted of the following, in thousands: September 30, 2021 December 31, 2020 Accounts payable $ 2,875 $ 2,753 Accrued clinical trial research and development expenses 1,923 4,080 Accrued other research and development expenses 7,158 5,581 Accrued compensation and benefits 6,436 7,016 Operating lease liability, current portion 2,250 2,089 Other accrued expenses 1,284 1,505 Total accounts payable and accrued expenses $ 21,926 $ 23,024

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities as of September 30, 2021 are as follows, in thousands: Year Ending December 31, 2021 (remaining) $ 572 2022 2,319 2023 2,375 2024 1,863 2025 929 Total lease payments 8,058 Less: imputed interest (705 ) Total operating lease liabilities $ 7,353

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Share-based Compensation Expense	The following table summarizes share-based compensation expense for all share-based compensation arrangements, in thousands: Three Months Ended Nine Months Ended September 30, September 30, 2021 2020 2021 2020 Research and development $ 2,059 $ 1,003 $ 5,277 $ 2,618 General and administrative 4,055 2,357 11,905 6,447 Total share-based compensation expense $ 6,114 $ 3,360 $ 17,182 $ 9,065

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Summary Of Significant Accounting Policies [Line Items]
Restricted cash pledged as collateral	$ 210	$ 210	$ 210	$ 210	$ 210
Total potentially dilutive securities	6,950,000	5,178,000	6,950,000	5,178,000
Collateral Pledged
Summary Of Significant Accounting Policies [Line Items]
Restricted cash pledged as collateral	$ 200		$ 200

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 39,183	$ 325,493	$ 76,955	$ 26,135
Restricted cash	210	210	210
Total	$ 39,393	$ 325,703	$ 77,165	$ 26,135

Investments - Investments Measu

Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Fair Value	$ 504,262	$ 307,827
Fair Value Measurements on Recurring Basis
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, Amortized Cost		317,237
Cash equivalents, Fair Value		317,237
Short-term investments, Amortized Cost	504,447	307,779
Short-term investments, Unrealized Gains	78	86
Short-term investments, Unrealized Losses	(263)	(38)
Short-term investments, Fair Value	504,262	307,827
Cash equivalents and Short-term investments, Amortized Cost	536,675	625,016
Cash equivalents and Short-term investments, Unrealized Gains	78	86
Cash equivalents and Short-term investments, Unrealized Losses	(263)	(38)
Cash equivalents and Short-term investments, Estimated Fair Value	$ 536,490	$ 625,064
Fair Value Measurements on Recurring Basis | Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 or less	1 or less
Cash equivalents, Amortized Cost	$ 32,228	$ 311,239
Cash equivalents, Fair Value	$ 32,228	$ 311,239
Fair Value Measurements on Recurring Basis | Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	3 or less	2 or less
Short-term investments, Amortized Cost	$ 199,250	$ 113,020
Short-term investments, Unrealized Gains	40	36
Short-term investments, Unrealized Losses	(126)	(36)
Short-term investments, Fair Value	$ 199,164	$ 113,020
Fair Value Measurements on Recurring Basis | U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	3 or less	1 or less
Short-term investments, Amortized Cost	$ 143,635	$ 88,409
Short-term investments, Unrealized Gains	38	50
Short-term investments, Unrealized Losses	(92)	(2)
Short-term investments, Fair Value	$ 143,581	$ 88,457
Fair Value Measurements on Recurring Basis | Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)		1 or less
Cash equivalents, Amortized Cost		$ 5,998
Cash equivalents, Fair Value		$ 5,998
Maturities (years)	1 or less	1 or less
Short-term investments, Amortized Cost	$ 129,418	$ 106,350
Short-term investments, Fair Value	$ 129,418	$ 106,350
Fair Value Measurements on Recurring Basis | Non U S Government And Supranational Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	3 or less
Short-term investments, Amortized Cost	$ 23,151
Short-term investments, Unrealized Losses	(30)
Short-term investments, Fair Value	$ 23,121
Fair Value Measurements on Recurring Basis | U.S. Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	2 or less
Short-term investments, Amortized Cost	$ 8,993
Short-term investments, Unrealized Losses	(15)
Short-term investments, Fair Value	$ 8,978

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)security	Dec. 31, 2020USD ($)
Investments All Other Investments [Abstract]
Short-term investments with maturities less than one year	$ 320,900	$ 242,600
Short-term investments with maturities between one to three years	$ 183,400	65,200
Short-term investments maturities, description	As of September 30, 2021 and December 31, 2020, short-term investments of $320.9 million and $242.6 million, respectively, had maturities less than one year, and short-term investments of $183.4 million and $65.2 million, respectively, had maturities between one to three years.
Available for sale debt securities allowance for credit losses	$ 0
Allowance for credit losses	0	$ 0
Available for sale debt securities gross unrealized loss positions for less than twelve months	$ 200,200
Number of available-for-sale securities | security	22

Fair Value Measurements - Sched

Fair Value Measurements - Schedule Of Fair Value Measurements, By Major Security Type (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 504,262	$ 307,827
Fair Value Measurements on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		317,237
Short-term investments	504,262	307,827
Cash equivalents and short-term investments	536,490	625,064
Fair Value Measurements on Recurring Basis | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		311,239
Short-term investments	143,581	88,457
Cash equivalents and short-term investments	175,809	399,696
Fair Value Measurements on Recurring Basis | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		5,998
Short-term investments	360,681	219,370
Cash equivalents and short-term investments	360,681	225,368
Fair Value Measurements on Recurring Basis | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	32,228	311,239
Fair Value Measurements on Recurring Basis | Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	32,228	311,239
Fair Value Measurements on Recurring Basis | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		5,998
Short-term investments	129,418	106,350
Fair Value Measurements on Recurring Basis | Commercial Paper | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		5,998
Short-term investments	129,418	106,350
Fair Value Measurements on Recurring Basis | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	199,164	113,020
Fair Value Measurements on Recurring Basis | Corporate Debt Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	199,164	113,020
Fair Value Measurements on Recurring Basis | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	143,581	88,457
Fair Value Measurements on Recurring Basis | U.S. Treasury Securities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	143,581	$ 88,457
Fair Value Measurements on Recurring Basis | Non U S Government And Supranational Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	23,121
Fair Value Measurements on Recurring Basis | Non U S Government And Supranational Debt Securities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	23,121
Fair Value Measurements on Recurring Basis | U S Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	8,978
Fair Value Measurements on Recurring Basis | U S Agency Bonds | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 8,978

Balance Sheet Detail - Summary

Balance Sheet Detail - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,409	$ 2,307
Less: accumulated depreciation	(678)	(286)
Property and equipment, net	2,731	2,021
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,532	1,169
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,016	862
Laboratory and Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 861	$ 276

Balance Sheet Detail - Summar_2

Balance Sheet Detail - Summary of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accounts payable	$ 2,875	$ 2,753
Accrued clinical trial research and development expenses	1,923	4,080
Accrued other research and development expenses	7,158	5,581
Accrued compensation and benefits	6,436	7,016
Operating lease liability, current portion	2,250	2,089
Other accrued expenses	1,284	1,505
Total accounts payable and accrued expenses	$ 21,926	$ 23,024

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2021	Jun. 30, 2021	Sep. 30, 2021	Nov. 01, 2018
Debt Instrument [Line Items]
Payment of fees related to extinguishment of debt			$ 611
Loss on extinguishment of debt			$ (212)
Silicon Valley Bank | Term Loan
Debt Instrument [Line Items]
Principal amount outstanding on loan				$ 7,500
Maximum borrowing capacity under term loans				$ 20,000
Term loan facility maturity date			May 1, 2023
Description of term loan payment terms			The Term Loan had a scheduled maturity date of May 1, 2023.
Repayments Of Debt	$ 6,600
Final Payment Amount	$ 600
Debt Instrument Interest Rate Stated Percentage	7.75%
Payment of fees related to extinguishment of debt	$ 30,000
Loss on extinguishment of debt		$ 200

Leases - Additional Information

Leases - Additional Information (Detail)	1 Months Ended				3 Months Ended		9 Months Ended
	May 31, 2021USD ($)	May 31, 2020USD ($)Option	Mar. 31, 2020USD ($)Option	Jan. 31, 2020	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jun. 30, 2020USD ($)
Lessee Lease Description [Line Items]
Operating lease right-of-use assets					$ 5,989,000		$ 5,989,000		$ 6,334,000
Operating leases, liability					7,353,000		7,353,000		7,700,000
Long-term operating lease liabilities					$ 5,103,000		$ 5,103,000		$ 5,638,000
Weighted-average discount rate					5.50%		5.50%		5.50%
Weighted-average remaining lease term					3 years 6 months		3 years 6 months		4 years 1 month 6 days
Total cash paid for amounts included in the measurement of lease liabilities, net of tenant improvement reimbursements							$ 1,500,000	$ 100,000
ROU assets obtained in exchange for operating lease liabilities							1,000,000	7,500,000
Total operating lease rent expense					$ 500,000	$ 500,000	1,500,000	1,400,000
ASC 842
Lessee Lease Description [Line Items]
Total operating lease rent expense					500,000	$ 500,000	$ 1,500,000	$ 1,200,000
San Diego Lease
Lessee Lease Description [Line Items]
Lease commencement date				May 31, 2020
Lease commencement amendment date		Aug. 1, 2020
Lease extended expiration date		Nov. 30, 2025
Operating lease, existence of option to extend		true
Description of operating lease, option to extend		a one-time option to extend for a period of five additional years.
Number of options to extend lease | Option		1
Lease agreement additional extended lease term		5 years
Lease, monthly minimum rent payable		$ 58,000
Operating lease rate of increase in annual rent		3.00%
Lease allowance		$ 1,000,000
Operating lease right-of-use assets			$ 2,200,000
Operating leases, liability			$ 2,200,000
Boston Lease
Lessee Lease Description [Line Items]
Lease commencement date			Apr. 1, 2020
Operating lease, existence of option to extend			true
Description of operating lease, option to extend			one-time option to extend the Boston Lease for a period of five additional years after the expiration of the initial lease term
Number of options to extend lease | Option			1
Lease agreement additional extended lease term			5 years
Lease, monthly minimum rent payable			$ 105,500
Operating lease rate of increase in annual rent			2.00%
Operating lease right-of-use assets										$ 5,100,000
Operating leases, liability										5,100,000
Lease expiration date			Jul. 31, 2024
Boston Lease | Letter of Credit
Lessee Lease Description [Line Items]
Letter of Credit			$ 200,000
Sublease
Lessee Lease Description [Line Items]
Operating lease right-of-use assets										300,000
Operating leases, liability										$ 300,000
Lease expiration date							Aug. 9, 2021
Sublease commencement date		Jun. 9, 2020
Sublease term		2 years
Sublease | One Year
Lessee Lease Description [Line Items]
Lease, monthly minimum rent payable	$ 16,000	$ 12,500
Morehouse Lease
Lessee Lease Description [Line Items]
Lease commencement date	Aug. 10, 2021
Lease, monthly minimum rent payable	$ 24,000
Operating lease rate of increase in annual rent	3.00%
Lease allowance	$ 106,000
Operating lease right-of-use assets					1,000,000		$ 1,000,000
Operating leases, liability					$ 1,000,000		$ 1,000,000
Lease expiration date	Aug. 31, 2025

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
2021 (remaining)	$ 572
2022	2,319
2023	2,375
2024	1,863
2025	929
Total lease payments	8,058
Less: imputed interest	(705)
Total operating lease liabilities	$ 7,353	$ 7,700

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 6,114	$ 3,360	$ 17,182	$ 9,065
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	2,059	1,003	5,277	2,618
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 4,055	$ 2,357	$ 11,905	$ 6,447

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized Expense	$ 55
Weighted average service period	2 years 7 months 6 days
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized Expense	$ 4.4
Weighted average service period	3 years 3 months 18 days