CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME
Revenue	$ 248,884	$ 217,073	$ 673,813	$ 572,510
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, and accretion)	204,301	164,287	567,610	469,938
Depreciation and depletion	18,789	23,460	56,683	23,052
Accretion	1,865	1,065	5,532	5,641
(Gain) loss on derivative financial instruments	(838)	1,068	3,102	(5,257)
Selling, general and administrative expenses	12,798	11,161	33,077	38,187
Impairments	0	312	0	4,499
Debt restructuring costs	0	4,499	23	4,499
Other operating costs	121	360	406	814
Total costs and expenses	237,036	206,212	666,433	541,373
Operating income (loss)	11,848	10,861	7,380	31,137
Other income (expense)
Interest income	147	46	304	116
Interest expense	(9,573)	(13,032)	(32,351)	(35,371)
Other, net	(98)	(165)	(546)	(760)
Total other income (expense)	(9,524)	(13,151)	(32,593)	(36,015)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	2,324	(2,290)	(25,213)	(4,878)
Income tax benefit (expense)	115	647	(36)	3,226
Income (loss) from unconsolidated affiliates, net of tax	138	59	771	(1,018)
Net income (loss)	2,577	(1,584)	(24,478)	(2,670)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service costs	(1,821)	(1,872)	(5,462)	(3,381)
Postretirement medical plan change		0	0	42,851
Income tax on postretirement medical and pension changes	0	(831)	0	(2,776)
Other comprehensive income (loss)	(1,821)	(2,703)	(5,462)	36,694
Total comprehensive income (loss)	$ 756	$ (4,287)	$ (29,940)	$ 34,024
Income (loss) per common share
Basic	$ 0.03	$ (0.03)	$ (0.34)	$ (0.04)
Diluted	$ 0.03	$ (0.03)	$ (0.34)	$ (0.04)
Weighted-average shares outstanding - basic	75,139	61,365	72,152	61,285
Weighted-average shares outstanding - diluted	76,890	61,365	72,152	61,285