Business Segment (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Business segments
Number of business segments | segment			1
Revenues	$ 43,727	$ 43,559	$ 119,714	$ 120,312
Depreciation, depletion and amortization	4,880	4,189	14,224	12,482
Gross profit (loss)	14,182	13,483	34,416	31,903
Operating profit (loss)	11,273	10,555	25,407	23,663
Identifiable assets, at period end	271,707	273,833	271,707	273,833	$ 247,037
Capital expenditures	3,022	8,063	13,621	20,423
Lime and limestone operations
Business segments
Depreciation, depletion and amortization	4,706	4,056	13,681	12,074
Gross profit (loss)	14,256	13,477	34,802	31,853
Operating profit (loss)	11,347	10,549	25,793	23,613
Identifiable assets, at period end	194,819	185,043	194,819	185,043
Capital expenditures	3,022	8,063	13,621	20,423
Other
Business segments
Depreciation, depletion and amortization	174	133	543	408
Gross profit (loss)	(74)	6	(386)	50
Operating profit (loss)	(74)	6	(386)	50
Identifiable assets, at period end	76,888	88,790	76,888	88,790
Lime and limestone operations | Lime and limestone operations
Business segments
Revenues	43,473	43,265	119,049	119,311
Natural gas interests | Other
Business segments
Revenues	$ 254	$ 294	$ 665	$ 1,001