Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues	$ 32,295	$ 32,603	$ 105,294	$ 114,052
Cost of sales	25,475	26,416	89,553	85,812
Gross profit	6,820	6,187	15,741	28,240
Earnings of unconsolidated operations	15,145	17,438	44,926	47,851
Operating expenses
Selling, general and administrative expenses	11,833	14,341	37,151	39,782
Amortization of intangible assets	734	715	2,303	2,243
Gain on sale of assets	0	(94)	(247)	(131)
Operating expenses	12,567	14,962	39,207	41,894
Operating profit	9,398	8,663	21,460	34,197
Other (income) expense
Interest expense	336	230	1,069	683
Interest income	(95)	(1,878)	(625)	(3,012)
Income from other unconsolidated affiliates	(18)	(327)	(230)	(972)
Closed mine obligations	395	383	1,219	1,079
Gain on equity securities	(35)	(108)	(351)	(1,067)
Other, net	(1,064)	(1,258)	(1,181)	(1,236)
Other (income) expense	(481)	(2,958)	(99)	(4,525)
Income before income tax provision	9,879	11,621	21,559	38,722
Income tax provision	1,857	1,357	1,321	5,465
Net income	$ 8,022	$ 10,264	$ 20,238	$ 33,257
Earnings per share:
Basic earnings per share (in dollars per share)	$ 1.14	$ 1.47	$ 2.88	$ 4.77
Diluted earnings per share (in dollars per share)	$ 1.14	$ 1.47	$ 2.88	$ 4.76
Basic weighted average shares outstanding (in shares)	7,036	6,991	7,019	6,973
Diluted weighted average shares outstanding (in shares)	7,036	6,991	7,035	6,992