Income Taxes Components of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current provision:
Federal									$ 195,249	$ 191,194	$ 181,011
State									59,319	50,815	45,488
Deferred expense (benefit):
Federal									(3,560)	(11,270)	(36,067)
State									(675)	(1,985)	(6,924)
Income tax expense	$ 54,825	$ 76,877	$ 65,047	$ 53,584	$ 53,697	$ 57,017	$ 54,974	$ 63,066	$ 250,333	$ 228,754	$ 183,508