Business Segments (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)
Business segments
Number of business segments \| segment	2
Revenues	$ 35,287
Depreciation, depletion and amortization	4,177	$ 4,236
Gross profit (loss)	7,037	8,238
Capital expenditures	7,620	4,208
Lime and limestone operations
Business segments
Depreciation, depletion and amortization	4,012	4,031
Gross profit (loss)	6,793	8,020
Capital expenditures	7,620	4,206
Natural gas interests
Business segments
Depreciation, depletion and amortization	165	205
Gross profit (loss)	244	218
Capital expenditures		2
Lime and limestone operations \| Lime and limestone operations
Business segments
Revenues	34,714
Natural gas interests \| Natural gas interests
Business segments
Revenues	$ 573
Before adoption of 606
Business segments
Revenues		36,153
Before adoption of 606 \| Lime and limestone operations \| Lime and limestone operations
Business segments
Revenues		35,517
Before adoption of 606 \| Natural gas interests \| Natural gas interests
Business segments
Revenues		$ 636

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
-Subparagraph (c)
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

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