Income Taxes (Reconciliation of Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory tax benefit	$ (120,335)	$ (420,671)	$ (253,001)
Federal tax reform changes - 2017 Tax Act	(63,675)	0	0
State tax benefit (net of federal benefit)	(3,286)	(17,549)	(21,583)
Change in valuation allowance	(2,727)	(5,059)	3,148
Employee share based compensation	8,190	0	0
Other	(1,137)	(893)	(3,715)
Total income tax benefit	$ (182,970)	$ (444,172)	$ (275,151)