Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenues	$ 173,421	$ 193,734
Cost of sales	133,416	155,545
Gross profit	40,005	38,189
Earnings of unconsolidated mines	12,648	12,553
Operating expenses
Selling, general and administrative expenses	46,259	46,416
Amortization of intangible assets	982	1,085
Operating expenses	47,241	47,501
Operating profit	5,412	3,241
Other expense (income)
Interest expense	1,505	2,125
Income from other unconsolidated affiliates	(303)	(1,172)
Closed mine obligations	376	402
Other, net, including interest income	53	479
Other (income) expense	1,631	1,834
Income before income tax provision	3,781	1,407
Income tax provision	979	380
Net income	$ 2,802	$ 1,027
Earnings Per Share [Abstract]
Basic earnings per share (in dollars per share)	$ 0.41	$ 0.14
Diluted earnings per share (in dollars per share)	0.41	0.14
Dividends per share (in dollars per share)	$ 0.2625	$ 0.2575
Basic weighted average shares outstanding (in shares)	6,857	7,189
Diluted weighted average shares outstanding (in shares)	6,885	7,208