Income Taxes (Income Tax Provision (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current income tax expense (benefit)
Federal	$ 0	$ (8,515)	$ (42,500)
State	(785)	160	(407)
Total current income tax benefit	(785)	(8,355)	(42,907)
Deferred income tax expense (benefit)
Federal	(521,519)	(1,853,517)	400,544
State	(21,866)	(78,662)	29,429
Total deferred income tax expense (benefit)	(543,385)	(1,932,179)	429,973
Total income tax expense (benefit)	$ (544,170)	$ (1,940,534)	$ 387,066