Income Taxes - Income Tax (Benefit) Expense Attributable to Income Before Income Taxes (Details) - 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
Components Of Income Tax Expense Benefit Continuing Operations [Abstract]
U.S. federal, Current									$ 0
U.S. state and local, Current									29	$ 1	$ (143)
Total, Current	$ 29				$ (4)		$ (1)	$ 6	29	1	(143)
U.S. federal, Deferred									(328,257)	361,152	58,527
U.S. state and local, Deferred									(10,449)	35,350	(24,527)
Total, Deferred	(164,316)	$ (134,781)	$ (61,975)	$ 22,366	166,052	$ 93,522	117,977	18,951	(338,706)	396,502	34,000
U.S. federal, Total									(328,257)	361,152	58,527
U.S. state and local, Total									(10,420)	35,351	(24,670)
Total income tax expense	$ (164,287)	$ (134,781)	$ (61,975)	$ 22,366	$ 166,048	$ 93,522	$ 117,976	$ 18,957	$ (338,677)	$ 396,503	$ 33,857