Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Allowance for losses and nondeductible accruals	$ 32,242	$ 53,967
Net operating loss carryforward	153,746	190,603
Alternative minimum tax and research and development tax credit carryforward	5,409	5,409
Deferred tax assets, total	191,397	249,979
Depreciation, depletion, amortization, and impairment	(324,874)	(440,690)
Net deferred tax liability	(133,477)	(190,711)
Current deferred tax asset	0	25,211
Non-current-deferred tax liability	$ (133,477)	$ (215,922)