Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amount
Income taxes computed at the federal statutory rate	$ 4,529	$ 8,730	$ 8,266
(Reduction) increase in taxes resulting from:
Benefit of reduced federal income tax rates		(7,447)
Statutory depletion in excess of cost depletion	(1,199)	(2,004)	(1,854)
Research and development tax credit	(1,775)	(1,433)	(167)
Manufacturing deduction		(674)	(666)
State income taxes, net of federal income tax benefit	178	235	202
Other	150	388	83
Income tax expense (benefit)	$ 1,883	$ (2,205)	$ 5,864
Percent of Pretax Income
Income taxes computed at the federal statutory rate (as a percent)	21.00%	35.00%	35.00%
(Reduction) increase in taxes resulting from (as a percent):
Benefit of reduced federal income tax rates (as a percent)		(29.90%)
Statutory depletion in excess of cost depletion (as a percent)	(5.60%)	(8.00%)	(7.90%)
Research and development tax credit (as a percent)	(8.20%)	(5.70%)	(0.70%)
Manufacturing deduction (as a percent)		(2.70%)	(2.80%)
State income taxes, net of federal income tax benefit (as a percent)	0.80%	0.90%	0.90%
Other (as a percent)	0.70%	1.60%	0.30%
Income tax expense (benefit) (as a percent)	8.70%	(8.80%)	24.80%
Deferred tax liabilities
Lime and limestone property, plant and equipment	$ 11,219	$ 11,023
Fair value liability of foreign exchange hedges		26
Natural gas interests drilling costs and equipment	1,475	1,622
Total	12,694	12,671
Deferred tax assets
Fair value liability of foreign exchange hedges	3
Other	326	297
Total	329	297
Deferred tax liabilities, net, Total	12,365	12,374
Current income taxes:
Prepaid expenses and other current assets		1,394
Accrued expenses	54
Deferred income taxes:
Deferred tax liabilities, net	12,365	12,374
Current income tax expense	1,863	5,407	$ 5,087
Deferred income tax expense (benefit)	20	(7,612)	777
Income tax expense (benefit)	1,883	$ (2,205)	$ 5,864
Federal
Operating loss carry forwards
Net operating loss carryforwards	$ 0