Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Statement [Abstract]
Revenues	$ 61,369	$ 45,896	$ 116,392	$ 91,001
Cost of sales	45,726	36,911	84,902	74,324
Gross profit	15,643	8,985	31,490	16,677
Earnings of unconsolidated operations	14,622	13,542	29,214	28,884
Contract termination settlement	14,000	0	14,000	0
Operating expenses
Selling, general and administrative expenses	15,841	12,878	30,625	26,641
Amortization of intangible assets	1,058	911	1,905	1,893
(Gain) loss on sale of assets	(2,317)	68	(2,453)	27
Operating expenses	14,582	13,857	30,077	28,561
Operating profit	29,683	8,670	44,627	17,000
Other (income) expense
Interest expense	496	359	1,009	715
Interest income	(195)	(100)	(340)	(220)
Closed mine obligations	377	364	757	747
Loss (gain) on equity securities	1,878	(1,262)	1,360	(2,085)
Other contract termination settlements	(16,882)	0	(16,882)	0
Other, net	(1,064)	(127)	(1,294)	(257)
Other (income) expense	(15,390)	(766)	(15,390)	(1,100)
Income before income tax provision	45,073	9,436	60,017	18,100
Income tax provision	7,893	2,931	10,255	2,634
Net income	$ 37,180	$ 6,505	$ 49,762	$ 15,466
Earnings per share:
Basic earnings per share (in dollars per share)	$ 5.07	$ 0.91	$ 6.83	$ 2.17
Diluted earnings per share (in dollars per share)	$ 5.07	$ 0.91	$ 6.79	$ 2.16
Basic weighted average shares outstanding (in shares)	7,330	7,153	7,286	7,123
Diluted weighted average shares outstanding (in shares)	7,330	7,153	7,325	7,147