Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues	$ 31,440	$ 21,941	$ 96,321	$ 78,341
Cost of sales	25,345	19,466	79,956	66,711
Gross profit	6,095	2,475	16,365	11,630
Earnings of unconsolidated operations	17,141	16,197	48,119	44,627
Operating expenses
Selling, general and administrative expenses	12,032	11,723	34,522	31,809
Amortization of intangible assets	714	435	2,212	1,641
Gain on sale of assets	(57)	(475)	(320)	(3,500)
Operating expenses	12,689	11,683	36,414	29,950
Operating profit	10,547	6,989	28,070	26,307
Other expense (income)
Interest expense	421	946	1,636	2,806
Income from other unconsolidated affiliates	(321)	(313)	(954)	(932)
Closed mine obligations	272	336	994	1,071
Other, net, including interest income	(483)	64	(825)	15
Other (income) expense	(111)	1,033	851	2,960
Income from continuing operations before income tax provision	10,658	5,956	27,219	23,347
Income tax provision from continuing operations	1,458	2,625	3,450	4,564
Income from continuing operations	9,200	3,331	23,769	18,783
Discontinued operations, net of tax expense of $236 and $2,655 in the three and nine months ended September 30, 2017, respectively.	0	5,067	0	1,381
Net income	$ 9,200	$ 8,398	$ 23,769	$ 20,164
Basic earnings per share:
Continuing operations (in dollars per share)	$ 1.33	$ 0.49	$ 3.43	$ 2.75
Discontinued operations (in dollars per share)	0.00	0.74	0.00	0.20
Basic earnings per share (in dollars per share)	1.33	1.23	3.43	2.95
Diluted earnings per share:
Continuing operations (in dollars per share)	1.33	0.49	3.43	2.74
Discontinued operations (in dollars per share)	0.00	0.74	0.00	0.20
Diluted earnings per share (in dollars per share)	1.33	1.23	3.43	2.94
Dividends per share (in dollars per share)	$ 0.1650	$ 0.2725	$ 0.495	$ 0.8125
Basic weighted average shares outstanding (in shares)	6,940	6,839	6,921	6,825
Diluted weighted average shares outstanding (in shares)	6,940	6,866	6,939	6,854