Business Segments (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business segments
Number of business segments | segment									2
Revenues	$ 35,239	$ 36,934	$ 36,518	$ 36,153	$ 34,166	$ 38,650	$ 32,880	$ 33,586	$ 144,844	$ 139,282	$ 130,837
Depreciation, depletion and amortization									16,340	15,931	15,784
Gross profit (loss)	7,752	$ 9,552	$ 8,838	$ 8,238	7,434	$ 10,569	$ 7,241	$ 7,848	34,380	33,092	28,714
Assets	228,446				210,159				228,446	210,159	196,499
Capital expenditures									21,337	17,664	11,459
Unallocated corporate assets and cash items
Business segments
Assets	88,011				76,376				88,011	76,376	62,256
Lime and limestone operations
Business segments
Revenues									142,612	137,190	128,390
Depreciation, depletion and amortization									15,694	15,063	14,910
Gross profit (loss)									33,652	33,032	28,400
Assets	133,350				126,015				133,350	126,015	125,703
Capital expenditures									21,335	17,649	11,444
Natural gas interests
Business segments
Revenues									2,232	2,092	2,447
Depreciation, depletion and amortization									646	868	874
Gross profit (loss)									728	60	314
Assets	$ 7,085				$ 7,768				7,085	7,768	8,540
Capital expenditures									$ 2	$ 15	$ 15