Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Valuation allowance	$ (120,666)	$ (114,136)
Deferred tax assets:
Net operating loss carryforwards	93,507	84,608
Federal and state tax credits	19,982	16,624
Deferred revenue		5,994
Stock-based compensation expense	6,732	4,481
Other	2,414	3,409
Deferred tax assets	122,635	115,116
Deferred tax liabilities:
Other	(1,969)	(980)
Deferred tax liabilities	$ (1,969)	$ (980)