Income Taxes - Reconciliation of Federal Statutory Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%	34.00%
State income taxes, net of federal benefit			5.73%
Change in valuation allowance	(22.12%)	(13.17%)	(27.97%)
Change in tax law			(11.85%)
Research and experimentation credits	3.81%	0.77%
Foreign rate differential	(1.84%)	(1.74%)
Stock-based compensation		(2.60%)
In process research and development		(3.92%)
Other	(0.85%)	(0.34%)	0.09%