Income Taxes (Reconciliation Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense (benefit) computed by applying the statutory rate	$ (11,290)		$ 21,059	$ (72,386)
State income tax expense (benefit), net of federal benefit	(1,882)		1,655	(5,687)
Deferred tax liability revaluation	0	[1]	(81,307)	0	[1]
Restricted stock shortfall	424		1,867	5,465
Non-controlling interest in Superior	(1,138)		0	0
Statutory depletion and other	(110)		(952)	1,414
Income tax expense (benefit)	$ (13,996)		$ (57,678)	$ (71,194)

[1] In 2017, the revaluation from the Tax Act.