Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Allowance for losses and nondeductible accruals	$ 56,479	$ 55,231
Net operating loss carryforward	140,863	54,901
Alternative minimum tax and research and development tax credit carryforward	5,409	25,991
Deferred tax assets, total	202,751	136,123
Depreciation, depletion, amortization, and impairment	(464,295)	(1,000,811)
Net deferred tax liability	(261,544)	(864,688)
Current deferred tax asset	14,206	11,527
Non-current-deferred tax liability	$ (275,750)	$ (876,215)