Income Taxes - Effect of Temporary Differences and Carryforwards (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 73,310	$ 63,442
Research and development tax credit carryforwards	12,636	8,491
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	633	613
Stock-based compensation	9,680	7,703
Other	10,179	8,347
Total deferred tax assets	106,438	88,596
Less: Valuation allowance	(106,438)	(88,596)	$ (68,661)	$ (88,453)
Net deferred tax assets	$ 0	$ 0