Share-Based Compensation - Schedule of Grant Date Fair Values of Awards Using Monte Carlo Simulation Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	25.50%	[1]
Expected volatility, maximum	29.50%	[1]
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free rate	1.20%
Expected term	2 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free rate	1.50%
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 volatility over the performance period to estimate appropriate expected volatilities.