CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME
Revenue	$ 195,728	$ 181,249
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, and accretion)	168,939	165,035
Depreciation and depletion	18,645	19,102
Accretion	1,821	2,582
(Gain) loss on derivative financial instruments	2,344	1,962
Selling, general and administrative expenses	10,714	13,775
Impairments	0	4,154
Debt restructuring costs	40	0
Other operating costs	176	284
Total costs and expenses	202,679	206,894
Operating income (loss)	(6,951)	(25,645)
Other income (expense)
Interest income	39	37
Interest expense	(12,912)	(11,051)
Other, net	(310)	(389)
Total other income (expense)	(13,183)	(11,403)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(20,134)	(37,048)
Income tax benefit (expense)	(300)	1,421
Income (loss) from unconsolidated affiliates, net of tax	326	(748)
Net income (loss)	(20,108)	(36,375)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service costs	(1,821)	362
Income tax on postretirement medical and pension changes	0	(971)
Other comprehensive income (loss)	(1,821)	(609)
Total comprehensive income (loss)	$ (21,929)	$ (36,984)
Income (loss) per common share
Basic	$ (0.3)	$ (0.59)
Diluted	$ (0.3)	$ (0.59)
Weighted-average shares outstanding - basic	66,132	61,191
Weighted-average shares outstanding - diluted	66,132	61,191