Income Taxes - Effect of Temporary Differences and Carryforwards (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 100,927	$ 73,310
Research and development tax credit carryforwards	9,513	12,636
Deferred tax assets, deferred lease liability	6,962	7,653
Stock-based compensation	5,161	9,680
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	648	633
Accruals and other	8,138	8,219
Total deferred tax assets before allowance	131,349	112,131
Less: Valuation allowance	(114,275)	(106,438)	$ (88,596)	$ (68,661)
Deferred tax assets, net	17,074	5,693
DeferredTaxLiabilitiesDebtDiscount	12,045	0
Deferred Tax Liabilities, Leasing Arrangements	5,029	5,693
Deferred Tax Liabilities, Gross	17,074	5,693
Deferred Tax Assets, Net	$ 0	$ 0