CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenues
Revenues (as a percent)	100.00%	100.00%	100.00%	100.00%
Cost of revenues
Labor and other operating expenses (as a percent)	55.30%	63.70%	55.40%	62.60%
Depreciation, depletion and amortization (as a percent)	8.00%	9.10%	8.30%	9.60%
Total cost of revenues (as a percent)	63.30%	72.80%	63.70%	72.20%
Gross profit (as a percent)	36.70%	27.20%	36.30%	27.80%
Selling, general and administrative expenses (as a percent)	5.90%	6.40%	6.00%	6.70%
Operating profit (as a percent)	30.80%	20.80%	30.30%	21.10%
Other expense (income)
Interest expense (as a percent)	0.10%	0.10%	0.10%	0.10%
Interest and other income, net (as a percent)	(2.60%)	(0.30%)	(2.50%)	(0.20%)
Total other expense (income) (as a percent)	(2.50%)	(0.20%)	(2.40%)	(0.10%)
Income before income tax expense (as a percent)	33.30%	21.00%	32.70%	21.20%
Income tax expense (as a percent)	6.70%	4.10%	6.50%	4.20%
Net income (as a percent)	26.60%	16.90%	26.20%	17.00%