Income Taxes - Income Tax Expense (Benefit) Attributable to Income Before Income Taxes (Details) (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
Components Of Income Tax Expense Benefit Continuing Operations [Abstract]
U.S. federal, Current
U.S. state and local, Current									1	(143)	(1,778)
Total, Current	(4)		(1)	6	(143)		(25)	25	1	(143)	(1,778)
U.S. federal, Deferred									361,152	58,527	11,873
U.S. state and local, Deferred									35,350	(24,527)	1,959
Total, Deferred	166,052	93,522	117,977	18,951	(28,180)	11,866	97,519	(47,205)	396,502	34,000	13,832
U.S. federal, Total									361,152	58,527	11,873
U.S. state and local, Total									35,351	(24,670)	181
Total income tax expense	$ 166,048	$ 93,522	$ 117,976	$ 18,957	$ (28,323)	$ 11,866	$ 97,494	$ (47,180)	$ 396,503	$ 33,857	$ 12,054