Income Taxes - Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax at statutory federal rate	21.00%	35.00%
State taxes	6.20%	1.70%
Permanent differences	(0.10%)	(3.00%)
Stock-based compensation	(0.40%)	(7.20%)
Tax Cuts and Jobs Act Impact	0.10%	(19.90%)
Tax credits	2.50%	11.60%
Change in deferred state tax rate		7.70%
Other		0.30%
Change in valuation allowance	(18.10%)	9.90%
Total	11.20%	36.10%