Unaudited Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Revenues	$ 55,023	$ 45,105
Cost of sales	39,176	37,413
Gross profit	15,847	7,692
Earnings of unconsolidated operations	14,592	15,342
Operating expenses
Selling, general and administrative expenses	14,784	13,763
Amortization of intangible assets	847	982
Gain on sale of assets	(136)	(41)
Operating expenses	15,495	14,704
Operating profit	14,944	8,330
Other (income) expense
Interest expense	513	356
Interest income	(145)	(120)
Closed mine obligations	380	383
Gain on equity securities	(518)	(823)
Other, net	(230)	(130)
Other (income) expense	0	(334)
Income before income tax provision (benefit)	14,944	8,664
Income tax provision (benefit)	2,362	(297)
Net income	$ 12,582	$ 8,961
Earnings per share:
Basic earnings per share (in dollars per share)	$ 1.73	$ 1.26
Diluted earnings per share (in dollars per share)	$ 1.72	$ 1.25
Basic weighted average shares outstanding (in shares)	7,253	7,101
Diluted weighted average shares outstanding (in shares)	7,321	7,142