Summary of Significant Accounting Policies - Additional Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Values of Financial Instruments
Foreign exchange hedges liabilities		$ (352)
Foreign exchange hedges assets	$ 111
Additions and write-offs to the company's allowance for doubtful accounts
Beginning balance	334	400
Additions	69	293
Write-offs	(57)	(359)
Ending balance	346	334	$ 400
Lime and limestone inventories:
Raw materials	5,105	4,811
Finished goods	2,266	2,070
Total	7,371	6,881
Service parts inventories	6,175	5,552
Total inventories	13,546	12,433
Supplemental cash flow information
Interest	140	113	948
Income taxes	6,718	4,908	4,152
Revenue Recognition
External freight billed to customers included in revenue	23,489	23,087	$ 20,145
Recurring | Fair value | Cash flows approach
Fair Values of Financial Instruments
Foreign exchange hedges liabilities		(352)
Foreign exchange hedges assets	111
Recurring | Significant Other Observable Inputs (Level 2) | Fair value | Cash flows approach
Fair Values of Financial Instruments
Foreign exchange hedges liabilities		$ (352)
Foreign exchange hedges assets	$ 111