CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Lime and limestone operations (as a percent)	98.60%	98.60%	98.50%	98.60%
Natural gas interests (as a percent)	1.40%	1.40%	1.50%	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)	62.70%	62.30%	64.30%	64.30%
Depreciation, depletion and amortization (as a percent)	11.50%	10.40%	11.40%	11.30%
Total cost of revenues (as a percent)	74.20%	72.70%	75.70%	75.60%
Gross profit (as a percent)	25.80%	27.30%	24.30%	24.40%
Selling, general and administrative expenses (as a percent)	7.20%	6.40%	6.90%	6.90%
Operating profit (as a percent)	18.60%	20.90%	17.40%	17.50%
Other expenses (income)
Interest expense (as a percent)	0.10%	0.20%	0.20%	0.10%
Other income, net (as a percent)	(0.70%)	(0.30%)	(0.60%)	(0.20%)
Total other expense (income) (as a percent)	(0.60%)	(0.10%)	(0.40%)	(0.10%)
Income before income taxes (as a percent)	19.20%	21.00%	17.80%	17.60%
Income tax expense (as a percent)	3.90%	5.30%	3.60%	4.40%
Net income (as a percent)	15.30%	15.70%	14.20%	13.20%