Income Taxes - Income Tax (Benefit) Expense Attributable to Income Before Income Taxes (Details) - 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
Components Of Income Tax Expense Benefit Continuing Operations [Abstract]
U.S. federal, Current									$ 0	$ 0	$ 0
U.S. state and local, Current									98	29	1
Total, Current	$ 98	$ 0	$ 0	$ 0	$ 29	$ 0	$ 0	$ 0	98	29	1
U.S. federal, Deferred									(266,105)	(328,257)	361,152
U.S. state and local, Deferred									(14,743)	(10,449)	35,350
Total, Deferred	(95,679)	(13,705)	(129,488)	(41,976)	(164,316)	(134,781)	(61,975)	22,366	(280,848)	(338,706)	396,502
U.S. federal, Total									(266,105)	(328,257)	361,152
U.S. state and local, Total									(14,645)	(10,420)	35,351
Total income tax (benefit) expense	$ (95,581)	$ (13,705)	$ (129,488)	$ (41,976)	$ (164,287)	$ (134,781)	$ (61,975)	$ 22,366	$ (280,750)	$ (338,677)	$ 396,503