Segment Information (Reconciliation Segment Income To Consolidated Income Before Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Information
Net income (loss)	$ (6,042)	$ (25,299)
Provision for (benefit from) income taxes	378	(1,791)
Interest expense, net	3,800	2,129
Depreciation, depletion and amortization	25,797	31,308
Accretion on asset retirement obligations	5,437	5,006
Costs related to proposed joint venture with Peabody Energy		3,664
Asset impairment and restructuring		5,828
Severance costs related to voluntary separation plan		5,800
Gain on property insurance recovery related to Mountain Laurel longwall		(9,000)
Preference Rights Lease Application settlement income		(9,000)
Non-service related pension and postretirement benefit costs	1,527	1,096
Reorganization items, net		(26)
Adjusted EBITDA	30,897	12,915
EBITDA from idled or otherwise disposed operations	3,566	5,099
Selling, general and administrative expenses	21,480	22,745
Other	(1,265)	59
Segment Adjusted EBITDA from coal operations	$ 54,678	$ 40,818