Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Allowance for losses and nondeductible accruals	$ 22,051	$ 31,822
Net operating loss carryforward	100,236	246,927
Depreciation, depletion, amortization, and impairment	80,947	0
Alternative minimum tax and research and development tax credit carryforward	1,738	2,656
Deferred tax assets, total	204,972	281,405
Depreciation, depletion, amortization, and impairment	0	(226,034)
Investment in Superior	(3,987)	(49,430)
Net deferred tax asset (liability)	200,985	5,941
Valuation allowance	(200,985)	(19,654)
Non-current-deferred tax liability	$ 0	$ (13,713)