CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME
Revenue (Note 3)	$ 168,451		$ 205,698		$ 313,528	$ 422,007
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, and accretion)	162,847		196,410		322,806	388,944
Depreciation and depletion	11,897		14,401		22,583	29,396
Accretion	1,493		1,706		3,097	3,411
(Gain) loss on derivative financial instruments	0		0		(1,809)	0
Selling, general and administrative expenses	14,963		12,975		33,535	20,292
Impairments (Note 6)	620,901		800		621,005	800
Other operating costs	111		55		351	183
Total costs and expenses	812,212		226,347		1,001,568	443,026
Operating income (loss)	(643,761)		(20,649)		(688,040)	(21,019)
Other income (expense)
Net periodic postretirement benefit income (cost), excluding service cost	1,755		1,617		3,510	3,235
Interest income	106		274		393	538
Interest expense (contractual interest of $8.6 M and $16.3 M for the three and six months ended June 30,2019, respectively)	(5,081)		(10,541)		(12,773)	(19,729)
Reorganization items, net (Note 7)	37,190		0		37,190	0
Other, net	(483)		(334)		(498)	(604)
Total other income (expense)	33,487		(8,984)		27,822	(16,560)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(610,274)		(29,633)		(660,218)	(37,579)
Income tax benefit (expense)	(35)		(234)		(74)	(297)
Income (loss) from unconsolidated affiliates, net of tax	630		(5)		866	266
Net income (loss)	(609,679)	$ (49,748)	(29,872)	$ (7,738)	(659,426)	(37,610)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service costs	0		(1,837)		0	(3,675)
Postretirement medical plan termination	(1,755)		0		(3,510)	0
Other comprehensive income (loss)	(1,755)		(1,837)		(3,510)	(3,675)
Total comprehensive income (loss)	$ (611,434)		$ (31,709)		$ (662,936)	$ (41,285)
Income (loss) per common share
Basic	$ (7.97)		$ (0.39)		$ (8.65)	$ (0.5)
Diluted	$ (7.97)		$ (0.39)		$ (8.65)	$ (0.5)
Weighted-average shares outstanding - basic	76,508		75,756		76,265	75,544
Weighted-average shares outstanding - diluted	76,508		75,756		76,265	75,544