Share-Based Compensation - Schedule of Grant Date Fair Values of Awards Using Monte Carlo Simulation Valuation Model (Detail)	9 Months Ended
	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected volatility, minimum	20.00%	[1]
Expected volatility, maximum	24.00%	[1]
Risk-free rate, minimum	2.40%
Risk-free rate, maximum	2.70%
Expected term	3 years

[1] Due to limited trading history of our common stock, we used the historical and implied volatilities of our peer group in addition to our historical and implied volatilities over the performance period to estimate appropriate expected volatilities.