CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME
Revenue	$ 317,553	$ 319,066
Costs and expenses
Cost of product sold (exclusive of depreciation, depletion, amortization, and accretion, shown separately)	264,317	271,939
Depreciation and depletion	24,536	26,928
Amortization	928	0
Accretion	3,541	4,130
Derivative financial instruments	4,785	(12,734)
Selling, general and administrative expenses	11,249	12,441
Other operating costs	213	238
Total costs and expenses	309,569	302,942
Operating income	7,984	16,124
Other income (expense)
Interest income	49	124
Interest expense	(12,668)	(37,994)
Other, net	(337)	(465)
Total other income (expense)	(12,956)	(38,335)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(4,972)	(22,211)
Income tax benefit (expense)	280	6,490
Earnings from unconsolidated affiliates, net of tax	12	95
Net income (loss)	(4,680)	(15,626)
Other comprehensive income (loss)
Postretirement medical plan amortization of prior service costs	313	247
Income tax on postretirement medical plan and pension adjustments	(116)	(89)
Other comprehensive income (loss)	197	158
Total comprehensive income (loss)	$ (4,483)	$ (15,468)
Earnings (Loss) per Share
Basic	$ (0.08)	$ (0.26)
Diluted	$ (0.08)	$ (0.26)
Weighted-average shares outstanding - basic (in shares)	60,935	60,741
Weighted-average shares outstanding - diluted (in shares)	60,935	60,741