Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 20,717	$ 10,942
Research and development credits	4,809	3,657
Depreciation and amortization	638	729
Accruals	558	569
Deferred rent	0	400
Lease liability	1,980
Stock-based compensation	331	213
Capital loss carryforwards	23	23
Other	8	2
Total gross deferred tax assets	29,064	16,535
Valuation allowance	(27,450)	(16,535)
Net deferred tax assets	1,614	0
Right-of-use assets	(1,614)
Net deferred tax assets	$ 0	$ 0