Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenues	$ 856,438	$ 915,860	$ 896,782
Cost of sales	650,585	736,364	711,710
Gross profit	205,853	179,496	185,072
Earnings of unconsolidated mines	55,238	48,432	48,396
Operating expenses
Selling, general and administrative expenses	197,903	193,925	198,697
Centennial asset impairment charge	17,443	0	105,119
Amortization of intangible assets	3,884	3,987	3,300
Loss (gain) on sale of assets	146	(1,811)	(7,339)
Operating Expenses	219,376	196,101	299,777
Operating profit (loss)	41,715	31,827	(66,309)
Other expense (income)
Interest expense	5,692	6,924	7,566
Income from other unconsolidated affiliates	(1,221)	(2,040)	(161)
Closed mine obligations	(214)	919	2,582
Other, net, including interest income	2,988	1,225	277
Other (income) expense	7,245	7,028	10,264
Income (loss) before income tax provision (benefit)	34,470	24,799	(76,573)
Income tax provision (benefit)	4,863	2,815	(38,455)
Net income (loss)	$ 29,607	$ 21,984	$ (38,118)
Basic earnings (loss) per share (USD per share)	$ 4.34	$ 3.14	$ (5.02)
Diluted earnings (loss) per share (USD per share)	$ 4.32	$ 3.13	$ (5.02)
Basic weighted average shares outstanding (in shares)	6,818	7,001	7,590
Diluted weighted average shares outstanding (in shares)	6,854	7,022	7,590