Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Allowance for losses and nondeductible accruals	$ 31,822	$ 27,953
Net operating loss carryforward	246,927	152,112
Alternative minimum tax and research and development tax credit carryforward	2,656	3,574
Deferred tax assets, total	281,405	183,639
Depreciation, depletion, amortization, and impairment	(226,034)	(291,542)
Investment in Superior	(49,430)	(36,845)
Net deferred tax asset (liability)	5,941	(144,748)
Valuation allowance	(19,654)	0
Current deferred tax asset	0	0
Non-current-deferred tax liability	$ (13,713)	$ (144,748)