Incentive Stock Options and Employee Stock Purchase Plan - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Stock-based compensation expense	$ 5,336	$ 6,014	$ 9,320	$ 9,186
Research and Development Expenses [Member]
Stock-based compensation expense	2,841	4,091	4,921	5,545
General and Administrative Expenses [Member]
Stock-based compensation expense	$ 2,495	$ 1,923	$ 4,399	$ 3,641

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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