Income Taxes - Deferred Income Tax (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets
Net operating loss carryforwards	$ 101,967	$ 76,753
Research and development tax credits	5,872	4,699
Reserves and accruals	5,720	1,444
Operating lease liability	3,088	0
Other	3,422	9,109
Total deferred tax assets	120,069	92,005
Less: Valuation allowance	(117,229)	(92,005)
Net deferred tax assets	2,840	0
Deferred tax liabilities
Right-of-use assets	(2,840)	0
Total deferred tax liabilities	(2,840)	0
Net deferred tax assets	$ 0	$ 0