Income Taxes (Schedule Of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Allowance for doubtful accounts	$ 1,713	$ 1,291
Operating loss and tax credit carryforwards	150,426	136,647
Compensation and employee benefits	27,625	35,532
Decommissioning liabilities	30,960	29,405
Operating leases	2,792	1,002
Other	34,578	24,903
Deferred tax assets, gross	248,094	228,780
Valuation allowance	(139,106)	(84,741)
Net deferred tax assets	108,988	144,039
Deferred tax liabilities:
Property, plant and equipment	69,510	114,024
Notes receivable	12,977	12,977
Goodwill and other intangible assets	23,920	20,285
Other	7,869
Deferred tax liabilities	114,276	147,286
Net deferred tax liability	$ 5,288	$ 3,247