Income Taxes (Reconciliation of Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal statutory tax expense (benefit)	$ (420,671)	$ (253,001)	$ 372,644
State tax expense (benefit) (net of federal benefit)	(17,549)	(21,583)	21,350
Change in valuation allowance	(5,059)	3,148	2,245
Research and development credit	0	(1,971)	0
Other	(893)	(1,744)	2,409
Income tax expense (benefit)	$ (444,172)	$ (275,151)	$ 398,648