UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Total revenues	$ 808,148	$ 858,563
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	560,536	606,666
Selling, general and administrative expenses	121,641	129,307
Accretion of environmental liabilities	2,953	2,561
Depreciation and amortization	72,163	74,533
Income from operations	50,855	45,496
Other expense, net	(1,228)	(2,365)
Loss on sale of businesses	0	(3,074)
Interest expense, net of interest income of $479 and $998, respectively	(17,918)	(18,787)
Income before provision for income taxes	31,709	21,270
Provision for income taxes	9,973	9,698
Net income	$ 21,736	$ 11,572
Earnings Per Share [Abstract]
Basic (in dollars per share)	$ 0.40	$ 0.21
Diluted (in dollars per share)	$ 0.39	$ 0.21
Shares used to compute earnings per share - Basic (in shares)	54,723	55,757
Shares used to compute earnings per share - Diluted (in shares)	55,043	56,055
Service revenues
Revenues:
Total revenues	$ 662,708	$ 719,867
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	450,338	492,716
Product revenues
Revenues:
Total revenues	145,440	138,696
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 110,198	$ 113,950