Income Taxes - Components of Provision for Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Current income tax expense, U.S. federal									$ (21,345)	$ 39,279	$ 126,585
Current income tax expense, State and local									(227)	4,611	22,004
Total current income tax expense									(21,572)	43,890	148,589
Deferred income tax (benefit), U.S. federal									39,227	(46,345)	(51,145)
Deferred income tax (benefit), State and local									2,742	(7,757)	(8,426)
Total Deferred income tax (benefit)									41,969	(54,102)	(59,571)
Total provision (benefit) for income taxes	$ 10,418	$ 7,278	$ 182	$ 2,519	$ (14,396)	$ 3,336	$ 6,503	$ (5,655)	$ 20,397	$ (10,212)	$ 89,018