Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Revenues	$ 196,500	$ 200,370	$ 390,234	$ 377,783
Cost of sales	161,119	163,847	316,664	305,089
Gross profit	35,381	36,523	73,570	72,694
Earnings of unconsolidated mines	12,076	11,567	24,629	24,005
Operating expenses
Selling, general and administrative expenses	45,219	50,990	91,635	99,419
Amortization of intangible assets	950	991	2,035	1,756
Operating expenses	46,169	51,981	93,670	101,175
Operating profit (loss)	1,288	(3,891)	4,529	(4,476)
Other expense (income)
Interest expense	1,661	1,950	3,786	3,404
Income from other unconsolidated affiliates	(300)	420	(1,472)	32
Closed mine obligations	425	308	827	624
Other, net, including interest income	(167)	(273)	312	(151)
Other (income) expense	1,619	2,405	3,453	3,909
Income (loss) before income tax provision (benefit)	(331)	(6,296)	1,076	(8,385)
Income tax provision (benefit)	(56)	(2,672)	324	(3,237)
Net income (loss)	$ (275)	$ (3,624)	$ 752	$ (5,148)
Earnings Per Share [Abstract]
Basic earnings (loss) per share (in dollars per share)	$ (0.04)	$ (0.47)	$ 0.11	$ (0.66)
Diluted earnings (loss) per share (in dollars per share)	(0.04)	(0.47)	0.11	(0.66)
Dividends per share (in dollars per share)	$ 0.2625	$ 0.2575	$ 0.52	$ 0.5075
Basic weighted average shares outstanding	7,048	7,712	7,114	7,777
Diluted weighted average shares outstanding	7,048	7,712	7,129	7,777