CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenues	$ 128,432	$ 140,990
Cost of sales	111,463	109,862
Gross profit	16,969	31,128
Earnings of unconsolidated operations	60,203	63,883
Operating expenses
Selling, general and administrative expenses	53,062	53,783
Amortization of intangible assets	2,572	2,614
Gain on sale of assets	(269)	(206)
Asset impairment charges	8,359	0
Operating expenses	63,724	56,191
Operating profit	13,448	38,820
Other (income) expense
Interest expense	1,354	872
Interest income	(1,200)	(3,616)
Income from other unconsolidated affiliates	(239)	(1,300)
Closed mine obligations	1,641	1,537
Gain on equity securities	(1,226)	(1,545)
Other, net	(1,140)	(527)
Other (income) expense	(810)	(4,579)
Income before income tax (benefit) provision	14,258	43,399
Income tax (benefit) provision	(535)	3,767
Net income	$ 14,793	$ 39,632
Earnings per share:
Basic earnings per share (USD per share)	$ 2.11	$ 5.68
Diluted earnings per share (USD per share)	$ 2.10	$ 5.66
Basic weighted average shares outstanding (in shares)	7,026	6,974
Diluted weighted average shares outstanding (in shares)	7,057	7,007