CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Revenues
Revenues (as a percent)	100.00%	100.00%
Cost of revenues
Labor and other operating expenses (as a percent)	61.40%	59.00%
Depreciation, depletion and amortization (as a percent)	10.20%	12.70%
Total cost of revenues (as a percent)	71.60%	71.70%
Gross profit (as a percent)	28.40%	28.30%
Selling, general and administrative expenses (as a percent)	7.10%	7.40%
Operating profit (as a percent)	21.30%	20.90%
Other expense (income)
Interest expense (as a percent)	0.10%	0.10%
Interest and other income, net (as a percent)	(0.10%)	(0.10%)
Income before income tax expense (as a percent)	21.30%	20.90%
Income tax expense (as a percent)	4.30%	4.00%
Net income (as a percent)	17.00%	16.90%