Income Taxes - Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 44,239	$ 29,025
Research and development tax credit carryforwards	5,220	3,385
Other	2,521	1,731
Total deferred tax assets	51,980	34,141
Valuation allowance	$ (51,980)	$ (34,141)	$ (24,519)