Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 211,641	$ 209,454	$ 180,895
State	37,006	38,095	36,142
Deferred:
Federal	60,785	(9,230)	2,681
State	(42)	(1,884)	567
Total	$ 309,390	$ 236,435	$ 220,285