Summary of Significant Accounting Policies - Additional Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Additions and write-offs to the company's allowance for doubtful accounts
Beginning balance	$ 361	$ 430
Additions	60	102
Write-offs	(23)	(171)
Ending balance	398	361	$ 430
Lime and limestone inventories:
Raw materials	4,279	4,546
Finished goods	2,866	1,954
Total	7,145	6,500
Service parts inventories	8,065	6,888
Total inventories	15,210	13,388
Supplemental cash flow information
Interest	152	150	179
Income taxes	975	445	331
Revenue Recognition
External freight billed to customers included in revenue	$ 28,373	28,397	$ 25,637
Recurring | Fair value | Cash flows approach
Fair Values of Financial Instruments
Foreign exchange hedges liabilities		(1)
Recurring | Significant Other Observable Inputs (Level 2) | Fair value | Cash flows approach
Fair Values of Financial Instruments
Foreign exchange hedges liabilities		$ (1)