Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Sales	$ 122,510	$ 203,958
Cost of goods sold (excluding depreciation, depletion and amortization)	106,751	138,653
Operating expenses
Selling, general and administrative	15,503	26,961
Depreciation, depletion and amortization	14,556	13,243
Total operating expenses	30,059	40,204
Operating income (loss)	(14,300)	25,101
Other income (expense)
Interest expense	(6,643)	(6,836)
Other income, net, including interest income	1,790	11
Total other (expenses) income	(4,853)	(6,825)
Income (loss) before income taxes	(19,153)	18,276
Income tax benefit (expense)	8,493	(3,453)
Net income (loss)	$ (10,660)	$ 14,823
Earnings (loss) per share:
Basic (in usd per share)	$ (0.20)	$ 0.28
Diluted (in usd per share)	$ (0.20)	$ 0.28
Weighted Average Number of Shares Outstanding, Basic	54,470	53,416
Weighted Average Number of Shares Outstanding, Diluted	54,470	53,869
Common stock cash dividend declared, per share	$ 0.0625	$ 0.13