Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenues	$ 915,860	$ 896,782	$ 932,666
Cost of sales	736,364	711,710	711,375
Gross profit	179,496	185,072	221,291
Earnings of unconsolidated mines	48,432	48,396	46,429
Operating expenses
Selling, general and administrative expenses	193,925	198,697	199,331
Centennial long-lived asset impairment charge	0	105,119	0
Centennial goodwill impairment charge	0	0	3,973
Amortization of intangible assets	3,987	3,300	3,668
(Gain) loss on sale of assets	(1,811)	(7,339)	(588)
Operating Expenses	196,101	299,777	206,384
Operating profit (loss)	31,827	(66,309)	61,336
Other expense (income)
Interest expense	6,924	7,566	4,775
Income from other unconsolidated affiliates	(2,040)	(161)	(1,432)
Closed mine obligations	919	2,582	1,817
Other, net, including interest income	1,225	277	456
Other (income) expense	7,028	10,264	5,616
Income (loss) before income tax provision (benefit)	24,799	(76,573)	55,720
Income tax provision (benefit)	2,815	(38,455)	11,270
Net income (loss)	$ 21,984	$ (38,118)	$ 44,450
Basic earnings (loss) per share (USD per share)	$ 3.14	$ (5.02)	$ 5.48
Diluted earnings (loss) per share (USD per share)	$ 3.13	$ (5.02)	$ 5.47
Basic weighted average shares outstanding (in shares)	7,001	7,590	8,105
Diluted weighted average shares outstanding (in shares)	7,022	7,590	8,124