CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 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)	59.40%	67.20%	63.10%	66.50%
Depreciation, depletion and amortization (as a percent)	9.60%	12.40%	10.40%	11.70%
Total cost of revenues (as a percent)	69.00%	79.60%	73.50%	78.20%
Gross profit (as a percent)	31.00%	20.40%	26.50%	21.80%
Selling, general and administrative expenses (as a percent)	6.80%	7.90%	6.80%	7.20%
Operating profit (as a percent)	24.20%	12.50%	19.70%	14.60%
Other (income) expense
Interest expense (as a percent)	0.10%	0.20%	0.20%	0.20%
Interest and other income, net (as a percent)	(1.10%)	(1.40%)	(1.20%)	(1.20%)
Total other (income) expense (as a percent)	(1.00%)	(1.20%)	(1.00%)	(1.00%)
Income before income tax expense (as a percent)	25.20%	13.70%	20.70%	15.60%
Income tax expense (as a percent)	2.50%	0.80%	3.20%	1.50%
Net income (as a percent)	22.70%	12.90%	17.50%	14.10%
Lime and limestone operations
Revenues
Total revenues (as a percent)	99.30%	98.40%	99.20%	98.30%
Natural gas interests
Revenues
Total revenues (as a percent)	0.70%	1.60%	0.80%	1.70%