CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenues
Revenues (as a percent)	100.00%	100.00%	100.00%	100.00%
Cost of revenues
Labor and other operating expenses (as a percent)	63.70%	55.30%	62.60%	57.00%
Depreciation, depletion and amortization (as a percent)	9.10%	10.50%	9.60%	11.50%
Total cost of revenues (as a percent)	72.80%	65.80%	72.20%	68.50%
Gross profit (as a percent)	27.20%	34.20%	27.80%	31.50%
Selling, general and administrative expenses (as a percent)	6.40%	6.00%	6.70%	6.60%
Operating profit (as a percent)	20.80%	28.20%	21.10%	24.90%
Other expense (income)
Interest expense (as a percent)	0.10%	0.20%	0.10%	0.10%
Interest and other income, net (as a percent)	(0.30%)	(0.20%)	(0.20%)	(0.10%)
Total other expense (income) (as a percent)	(0.20%)	0.00%	(0.10%)	0.00%
Income before income tax expense (as a percent)	21.00%	28.20%	21.20%	24.90%
Income tax expense (as a percent)	4.10%	5.60%	4.20%	4.90%
Net income (as a percent)	16.90%	22.60%	17.00%	20.00%