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Business Segments (Details) $ in Thousands	3 Months Ended								12 Months Ended
Business Segments (Details) $ in Thousands	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business segments
Number of business segments \| segment									2
Revenues									$ 144,435	$ 144,844	$ 139,282
Depreciation, depletion and amortization									17,391	16,340	15,931
Gross profit (loss)	$ 6,616	$ 7,196	$ 9,637	$ 7,037	$ 7,752	$ 9,552	$ 8,838	$ 8,238	30,486	34,380	33,092
Assets	244,671				228,446				244,671	228,446	210,159
Capital expenditures									53,762	21,337	17,664
Unallocated corporate assets and cash items
Business segments
Assets	68,893				88,011				68,893	88,011	76,376
Lime and limestone operations
Business segments
Depreciation, depletion and amortization									16,741	15,694	15,063
Gross profit (loss)									29,482	33,652	33,032
Assets	169,182				133,350				169,182	133,350	126,015
Capital expenditures									53,762	21,335	17,649
Natural gas interests
Business segments
Depreciation, depletion and amortization									650	646	868
Gross profit (loss)									1,004	728	60
Assets	$ 6,596				$ 7,085				6,596	7,085	7,768
Capital expenditures										2	15
Lime and limestone operations \| Lime and limestone operations
Business segments
Revenues									141,922	142,612	137,190
Natural gas interests \| Natural gas interests
Business segments
Revenues									$ 2,513	$ 2,232	$ 2,092