Business Segment (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Business segments
Number of business segments | segment			1
Revenues	$ 37,547	$ 38,954	$ 75,987	$ 76,753
Depreciation, depletion and amortization	4,743	4,225	9,344	8,293
Gross profit (loss)	10,357	9,727	20,234	18,420
Operating profit (loss)	7,476	7,088	14,134	13,108
Identifiable assets, at period end	259,270	261,473	259,270	261,473	$ 247,037
Capital expenditures	4,493	6,676	10,599	12,360
Lime and limestone operations
Business segments
Depreciation, depletion and amortization	4,563	4,089	8,975	8,018
Gross profit (loss)	10,507	9,690	20,546	18,376
Operating profit (loss)	7,626	7,051	14,446	13,064
Identifiable assets, at period end	184,397	179,780	184,397	179,780
Capital expenditures	4,493	6,676	10,599	12,360
Other
Business segments
Depreciation, depletion and amortization	180	136	369	275
Gross profit (loss)	(150)	37	(312)	44
Operating profit (loss)	(150)	37	(312)	44
Identifiable assets, at period end	74,873	81,693	74,873	81,693
Lime and limestone operations | Lime and limestone operations
Business segments
Revenues	37,362	38,581	75,576	76,046
Natural gas interests | Other
Business segments
Revenues	$ 185	$ 373	$ 411	$ 707