UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Statement [Abstract]
Revenues	$ 52,345	$ 61,350	$ 105,634	$ 111,491
Cost of sales	45,327	54,943	91,598	101,727
Gross profit	7,018	6,407	14,036	9,764
Earnings of unconsolidated operations	13,592	11,084	26,899	24,908
Operating expenses
Selling, general and administrative expenses	17,720	14,746	33,173	29,622
Amortization of intangible assets	116	927	242	1,654
(Gain) loss on sale of assets	(4,592)	68	(4,603)	(168)
Operating expenses	13,244	15,741	28,812	31,108
Operating profit	7,366	1,750	12,123	3,564
Other expense (income)
Interest expense	1,311	572	2,422	1,117
Interest income	(1,038)	(1,714)	(2,165)	(2,869)
Closed mine obligations	471	433	926	842
Loss (gain) on equity securities	264	(421)	(777)	(1,049)
Other, net	130	(377)	(84)	(2,102)
Other (income) expense	1,138	(1,507)	322	(4,061)
Income before income tax provision (benefit)	6,228	3,257	11,801	7,625
Income tax provision (benefit)	256	737	1,259	(587)
Net income	$ 5,972	$ 2,520	$ 10,542	$ 8,212
Earnings per share:
Basic earnings per share (in dollars per share)	$ 0.81	$ 0.34	$ 1.42	$ 1.10
Diluted earnings per share (in dollars per share)	$ 0.81	$ 0.34	$ 1.42	$ 1.09
Basic weighted average shares outstanding (in shares)	7,394	7,513	7,419	7,465
Diluted weighted average shares outstanding (in shares)	7,394	7,513	7,437	7,515