Share-Based Compensation - Schedule of Fair Value of Stock Option Award Granted Estimated on Date of Grant Using the Black-Scholes-Merton Option Pricing Model (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.60%	1.90%	1.30%
Weighted average volatility	56.10%	64.20%	70.40%
Expected life (in years)	5 years	5 years 2 months 12 days	4 years 9 months 18 days
Weighted average grant date fair value per share of options granted	$ 7.09	$ 4.81	$ 2.75