Income Taxes - Schedule of Significant Components of Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Valuation allowance	$ (114,136)	$ (89,815)
Deferred tax assets:
Net operating loss carryforwards	84,608	73,578
Federal and state tax credits	16,624	11,108
Deferred revenue	5,994	1,111
Stock-based compensation expense	4,481	3,605
Other	3,409	420
Deferred tax asset	115,116	89,822
Deferred tax liabilities:
Other	(980)	(7)
Deferred tax liabilities	$ (980)	$ (7)