Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Remeasurement of net deferred tax assets due to enactment of Tax Cut and Jobs Act	$ 62,702	$ 0	$ 0
Excess tax benefits from equity-based compensation	58,681	0	$ 0
Estimated federal taxable income	$ 614,562	$ 578,882
Statutory federal income tax rate	35.00%
Effective tax rate	36.53%	35.73%	36.52%
Unrecognized tax benefits that would affect effective tax rate	$ 35,816
Reversal of accrued interest on unrecognized tax benefits	1,065	$ 1,582
Unrecognized tax benefits expense				$ 125
Total accrued interest on unrecognized tax benefits	18,575	$ 19,639
Reduction in unrecognized tax benefits	$ 11,971