Business Segments (Details) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)
Business segments
Number of business segments \| segment			2
Revenues	$ 39,242		$ 74,529
Depreciation, depletion and amortization	4,288	$ 4,054	8,465	$ 8,290
Gross profit (loss)	9,637	8,838	16,674	17,076
Capital expenditures	5,333	4,376	19,378	8,585
Lime and limestone operations
Business segments
Depreciation, depletion and amortization	4,129	3,855	8,141	7,886
Gross profit (loss)	9,327	8,722	16,120	16,742
Capital expenditures	5,333	4,376	19,378	8,583
Natural gas interests
Business segments
Depreciation, depletion and amortization	159	199	324	404
Gross profit (loss)	310	116	554	334
Capital expenditures				2
Lime and limestone operations \| Lime and limestone operations
Business segments
Revenues	38,557		73,271
Natural gas interests \| Natural gas interests
Business segments
Revenues	$ 685		$ 1,258
Before adoption of 606
Business segments
Revenues		36,518		72,671
Before adoption of 606 \| Lime and limestone operations \| Lime and limestone operations
Business segments
Revenues		35,965		71,482
Before adoption of 606 \| Natural gas interests \| Natural gas interests
Business segments
Revenues		$ 553		$ 1,189

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1,2)
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The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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