Stock-Based Compensation - Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rates, Minimum	1.42%	2.82%	1.42%	2.67%
Risk-free interest rates, Maximum	1.90%	2.96%	2.67%	2.96%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	7 years 2 months 12 days	6 years	6 years 2 months 12 days	6 years
Expected volatility, Minimum	67.10%	71.30%	67.10%	69.80%
Expected volatility, Maximum	67.50%	72.10%	69.50%	72.10%