CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Coal revenues	$ 399,954	$ 523,987	$ 1,278,935	$ 1,784,775
Other revenues	737	1,877	4,054	6,409
Total revenues	400,691	525,864	1,282,989	1,791,184
Costs and expenses:
Cost of coal sales (exclusive of items shown separately below)	367,277	467,658	1,148,416	1,480,098
Depreciation, depletion and amortization	50,739	60,842	154,466	184,927
Accretion on asset retirement obligations	9,127	6,846	23,806	19,925
Amortization of acquired intangibles, net	2,219	2,314	5,180	(4,712)
Asset impairment and restructuring	3,571	32	221,453	5,858
Selling, general and administrative expenses (exclusive of depreciation, depletion and amortization shown separately above)	14,501	17,387	42,010	53,121
Merger-related costs	0	68	0	1,055
Total other operating (income) loss:
Mark-to-market adjustment for acquisition-related obligations	3,624	(3,238)	(13,425)	(288)
Other (income) expense	(1,359)	166	(2,063)	(7,319)
Total costs and expenses	449,699	552,075	1,579,843	1,732,665
(Loss) income from operations	(49,008)	(26,211)	(296,854)	58,519
Other income (expense):
Interest expense	(18,389)	(18,847)	(54,808)	(50,079)
Interest income	378	1,763	6,889	5,584
Loss on modification and extinguishment of debt	0	0	0	(26,459)
Equity loss in affiliates	(1,295)	(1,845)	(3,085)	(4,804)
Miscellaneous loss, net	(368)	(1,523)	(1,088)	(2,912)
Total other expense, net	(19,674)	(20,452)	(52,092)	(78,670)
Loss from continuing operations before income taxes	(68,682)	(46,663)	(348,946)	(20,151)
Income tax benefit	45	3,102	2,200	8,880
Net loss from continuing operations	(68,637)	(43,561)	(346,746)	(11,271)
Discontinued operations:
Loss from discontinued operations before income taxes	0	(11,516)	0	(176,973)
Income tax (expense) benefit from discontinued operations	0	(13,455)	0	12,866
Loss from discontinued operations	0	(24,971)	0	(164,107)
Net loss	$ (68,637)	$ (68,532)	$ (346,746)	$ (175,378)
Earnings Per Share, Basic [Abstract]
(Loss) income from continuing operations (in dollars per share)	$ (3.75)	$ (2.29)	$ (18.96)	$ (0.59)
Loss from discontinued operations (in dollars per share)	0	(1.31)	0	(8.63)
Net loss (in dollars per share)	(3.75)	(3.60)	(18.96)	(9.22)
Earnings Per Share, Diluted [Abstract]
(Loss) income from continuing operations (in dollars per share)	(3.75)	(2.29)	(18.96)	(0.59)
Loss from discontinuing operations (in dollars per share)	0	(1.31)	0	(8.63)
Net loss (in dollars per share)	$ (3.75)	$ (3.60)	$ (18.96)	$ (9.22)
Weighted average shares - basic (in shares)	18,319,947	19,025,462	18,290,346	19,014,974
Weighted average shares - diluted (in shares)	18,319,947	19,025,462	18,290,346	19,014,974
Revenue from Contract with Customer, Product and Service [Extensible List]	us-gaap:PublicUtilitiesInventoryCoalMember	us-gaap:PublicUtilitiesInventoryCoalMember	us-gaap:PublicUtilitiesInventoryCoalMember	us-gaap:PublicUtilitiesInventoryCoalMember