Income Taxes - Components of Provision for Income Tax Expense (Benefit) (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									$ 228,505	$ 215,950	$ 137,573
State									24,336	26,057	43,282
Total current provision									252,841	242,007	180,855
Deferred (benefit)/provision:
Federal									(89,518)	(69,546)	(40,370)
State									786	(7,681)	(518)
Total deferred (benefit)/provision									(88,732)	(77,227)	(40,888)
Provision for income tax expense	$ 43,122	$ 47,557	$ 34,555	$ 38,875	$ 54,915	$ 17,985	$ 60,158	$ 31,722	$ 164,109	$ 164,780	$ 139,967