Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement [Abstract]
Revenues	$ 61,793	$ 51,742	$ 178,185	$ 142,743
Cost of sales	43,965	37,413	128,867	111,737
Gross profit	17,828	14,329	49,318	31,006
Earnings of unconsolidated operations	14,588	17,652	43,802	46,536
Contract termination settlement	0	10,333	14,000	10,333
Operating expenses
Selling, general and administrative expenses	17,790	13,830	48,415	40,471
Amortization of intangible assets	867	902	2,772	2,795
(Gain) loss on sale of assets	2	(10)	(2,451)	17
Asset impairment charges	3,939	0	3,939	0
Operating expenses	22,598	14,722	52,675	43,283
Operating profit	9,818	27,592	54,445	44,592
Other (income) expense
Interest expense	486	493	1,495	1,208
Interest income	(352)	(101)	(692)	(321)
Closed mine obligations	398	372	1,155	1,119
Loss (gain) on equity securities	316	(445)	1,676	(2,530)
Income from equity method investee	(2,156)	0	(2,156)	0
Other contract termination settlements	0	0	(16,882)	0
Other, net	(354)	(161)	(1,648)	(418)
Other (income) expense	(1,662)	158	(17,052)	(942)
Income before income tax provision	11,480	27,434	71,497	45,534
Income tax provision	866	2,597	11,121	5,231
Net income	$ 10,614	$ 24,837	$ 60,376	$ 40,303
Earnings per share:
Basic earnings per share (in dollars per share)	$ 1.45	$ 3.47	$ 8.27	$ 5.65
Diluted earnings per share (in dollars per share)	$ 1.45	$ 3.47	$ 8.24	$ 5.63
Basic weighted average shares outstanding (in shares)	7,337	7,165	7,302	7,136
Diluted weighted average shares outstanding (in shares)	7,337	7,165	7,329	7,153