Employee Benefit Plans - Schedule of Weighted Average Grant Date Fair Value Per Share of Performance-Based and Market-Based RSUs and Assumptions Used to Estimate Fair Value (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Performance-based RSUs [Member] | Short-term.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share	$ 47.18	$ 39.79	$ 38.77
Service period (years)	1 year	1 year	1 year
Performance-based RSUs [Member] | Long-term.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share	$ 33.43	$ 45.76	$ 42.82
Service period, lower range (years)	2 years	2 years	2 years
Service period, upper range (years)	3 years	3 years	3 years
Market-based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value per share			$ 33.84
Derived service period (years)			1 year 7 months 6 days
Implied volatility			30.00%
Risk-free interest rate			1.70%