CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues
Lime and limestone operations (as a percent)	98.50%	98.50%	98.40%	98.60%
Natural gas interests (as a percent)	1.50%	1.50%	1.60%	1.40%
Total revenues (as a percent)	100.00%	100.00%	100.00%	100.00%
Cost of revenues
Labor and other operating expenses (as a percent)	64.70%	66.00%	65.10%	65.50%
Depreciation, depletion and amortization (as a percent)	11.10%	12.00%	11.40%	11.80%
Total cost of revenues (as a percent)	75.80%	78.00%	76.50%	77.30%
Gross profit (as a percent)	24.20%	22.00%	23.50%	22.70%
Selling, general and administrative expenses (as a percent)	6.90%	7.00%	6.80%	7.10%
Operating profit (as a percent)	17.30%	15.00%	16.70%	15.60%
Other expenses (income)
Interest expense (as a percent)	0.10%	0.20%	0.20%	0.20%
Other income, net (as a percent)	(0.60%)	(0.20%)	(0.60%)	(0.20%)
Total other expense (income) (as a percent)	(0.50%)	0.00%	(0.40%)	0.00%
Income before income taxes (as a percent)	17.80%	15.00%	17.10%	15.60%
Income tax expense (as a percent)	3.30%	3.80%	3.50%	3.90%
Net income (as a percent)	14.50%	11.20%	13.60%	11.70%