Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amount
Income taxes computed at the federal statutory rate	$ 7,155	$ 6,489	$ 4,529
(Reduction) increase in taxes resulting from:
Statutory depletion in excess of cost depletion	(1,266)	(1,200)	(1,199)
Research and development tax credit		(1,155)	(1,775)
State income taxes, net of federal income tax benefit	(262)	155	178
Other	222	555	150
Income tax expense	$ 5,849	$ 4,844	$ 1,883
Percent of Pretax Income
Income taxes computed at the federal statutory rate (as a percent)	21.00%	21.00%	21.00%
(Reduction) increase in taxes resulting from (as a percent):
Statutory depletion in excess of cost depletion (as a percent)	(3.70%)	(3.90%)	(5.60%)
Research and development tax credit (as a percent)		(3.70%)	(8.20%)
State income taxes, net of federal income tax benefit (as a percent)	(0.80%)	0.50%	0.80%
Other (as a percent)	0.70%	1.80%	0.70%
Income tax expense (as a percent)	17.20%	15.70%	8.70%
Deferred tax liabilities
Lime and limestone property, plant and equipment	$ 21,297	$ 16,928
Operating lease right-of-use assets	513	735
Natural gas interests drilling costs and equipment	519	1,040
Total	22,329	18,703
Deferred tax assets
Operating lease liabilities	511	728
Other	287	757
Total	798	1,485
Deferred tax liabilities, net, Total	21,531	17,218
Current income taxes:
Prepaid expenses and other current assets		416
Accrued expenses	990
Current income tax expense (benefit)	1,537	(4)	$ 1,863
Deferred income tax expense	4,312	4,848	20
Income tax expense	5,849	$ 4,844	$ 1,883
Federal
Operating loss carry forwards
Net operating loss carryforwards	$ 0