CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues
Total revenues (as a percent)	100.00%	100.00%	100.00%	100.00%
Cost of revenues
Labor and other operating expenses (as a percent)	64.20%	64.50%	65.20%	66.30%
Depreciation, depletion and amortization (as a percent)	10.80%	11.00%	10.70%	11.40%
Total cost of revenues (as a percent)	75.00%	75.50%	75.90%	77.60%
Gross profit (as a percent)	25.00%	24.50%	24.10%	22.40%
Selling, general and administrative expenses (as a percent)	6.80%	6.50%	6.90%	6.80%
Operating profit (as a percent)	18.20%	18.00%	17.20%	15.60%
Other (income) expense
Interest expense (as a percent)	0.20%	0.20%	0.20%	0.20%
Interest and other income, net (as a percent)	(1.30%)	(1.20%)	(1.20%)	(1.10%)
Total other (income) expense (as a percent)	(1.10%)	(1.00%)	(1.00%)	(0.90%)
Income before income tax expense (as a percent)	19.30%	19.00%	18.20%	16.50%
Income tax expense (as a percent)	3.80%	2.10%	3.70%	1.90%
Net income (as a percent)	15.50%	16.90%	14.50%	14.60%
Lime and limestone operations
Revenues
Total revenues (as a percent)	99.00%	98.30%	99.10%	98.30%
Natural gas interests
Revenues
Total revenues (as a percent)	1.00%	1.70%	0.90%	1.70%