Income Taxes (Reconciliation Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income tax expense (benefit) computed by applying the statutory rate	$ (72,386)	$ (582,508)	$ 78,029
State income tax expense (benefit), net of federal benefit	(5,687)	(45,768)	6,131
Restricted stock shortfall	5,465	0	0
Statutory depletion and other	1,414	1,328	2,503
Total Income tax expense (benefit)	$ (71,194)	$ (626,948)	$ 86,663