Income Taxes - Components of Provision for Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current provision:
Federal									$ 215,950	$ 137,573	$ 130,854
State									26,057	43,282	13,513
Total current provision									242,007	180,855	144,367
Deferred (benefit)/provision:
Federal									(69,546)	(40,370)	13,240
State									(7,681)	(518)	1,327
Total deferred (benefit)/provision									(77,227)	(40,888)	14,567
Provision for income tax expense	$ 54,915	$ 17,985	$ 60,158	$ 31,722	$ 24,465	$ 54,903	$ 31,941	$ 28,658	$ 164,780	$ 139,967	$ 158,934