UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Total revenues	$ 779,344	$ 891,668	$ 2,347,907	$ 2,541,185
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	511,629	612,754	1,588,976	1,772,051
Selling, general and administrative expenses	106,544	122,301	339,690	361,033
Accretion of environmental liabilities	2,822	2,490	8,149	7,624
Depreciation and amortization	74,470	73,756	221,497	223,328
Income from operations	83,879	80,367	189,595	177,149
Other income (expense), net	2,268	(427)	(597)	1,992
Loss on sale of businesses	(118)	0	(3,376)	0
Loss on early extinguishment of debt	0	(6,119)	0	(6,119)
Interest expense, net of interest income of $1,236, $1,152, $2,902 and $2,981, respectively	(17,407)	(19,702)	(54,848)	(59,681)
Income before provision for income taxes	68,622	54,119	130,774	113,341
Provision for income taxes	13,712	17,750	35,269	39,752
Net income	$ 54,910	$ 36,369	$ 95,505	$ 73,589
Earnings Per Share [Abstract]
Basic (in USD per share)	$ 0.99	$ 0.65	$ 1.72	$ 1.32
Diluted (in USD per share)	$ 0.99	$ 0.65	$ 1.71	$ 1.31
Shares used to compute earnings per share - Basic (in shares)	55,592	55,850	55,646	55,858
Shares used to compute earnings per share - Diluted (in shares)	55,738	56,165	55,832	56,109
Service revenues
Revenues:
Total revenues	$ 681,306	$ 739,919	$ 2,039,012	$ 2,111,662
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	428,735	496,005	1,332,516	1,439,717
Product revenues
Revenues:
Total revenues	98,038	151,749	308,895	429,523
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 82,894	$ 116,749	$ 256,460	$ 332,334