Income Taxes (Reconciliation Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income tax expense (benefit) computed by applying the statutory rate	$ (582,508)	$ 78,029	$ 105,514
State income tax, net of federal benefit	(45,768)	6,131	8,290
Statutory depletion and other	1,328	2,503	2,919
Income tax expense (benefit)	$ (626,948)	$ 86,663	$ 116,723