Income Taxes (Reconciliation Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2020	Aug. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense (benefit) computed by applying the statutory rate	$ (3,001)	$ (190,103)	$ (144,092)
State income tax expense (benefit), net of federal benefit	(500)	(31,684)	(21,733)
Deferred tax liability revaluation	0	0	0
Restricted stock shortfall	0	7,404	347
Non-controlling interest in Superior	(1,017)	7,504	(11)
Goodwill impairment	0	0	12,346
Valuation allowance	4,047	177,284	19,654
Reorganization adjustments	0	14,152	0
Statutory depletion and other	169	813	1,163
Income tax benefit	$ (302)	$ (14,630)	$ (132,326)