Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Allowance for losses and nondeductible accruals	$ 27,953		$ 32,242
Net operating loss carryforward	152,112		153,746
Alternative minimum tax and research and development tax credit carryforward	3,574		5,409
Deferred tax assets, total	183,639		191,397
Depreciation, depletion, amortization, and impairment	(291,542)		(324,874)
Investment in Superior	(36,845)		0
Net deferred tax liability	(144,748)		(133,477)
Current deferred tax asset	0		0
Non-current-deferred tax liability	$ (144,748)	$ (133,064)	$ (133,477)