UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 849,140	$ 752,788	$ 1,598,918	$ 1,441,729
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	583,584	519,803	1,130,009	1,016,388
Selling, general and administrative expenses	125,995	112,294	241,083	224,515
Accretion of environmental liabilities	2,448	2,416	4,878	4,706
Depreciation and amortization	72,760	71,531	147,604	143,943
Income from operations	64,353	46,744	75,344	52,177
Other income (expense), net	846	(833)	547	(2,382)
Loss on early extinguishment of debt	0	(6,045)	0	(6,045)
Gain on sale of business	0	31,722	0	31,722
Interest expense, net of interest income of $587, $311, $1,350 and $520, respectively	(20,769)	(22,492)	(41,039)	(45,068)
Income before (benefit) provision for income taxes	44,430	49,096	34,852	30,404
Provision for income taxes	13,683	23,216	16,736	25,917
Net income	$ 30,747	$ 25,880	$ 18,116	$ 4,487
Earnings per share:
Basic (in USD per share)	$ 0.55	$ 0.45	$ 0.32	$ 0.08
Diluted (in USD per share)	$ 0.54	$ 0.45	$ 0.32	$ 0.08
Shares used to compute loss per share - Basic (in shares)	56,410	57,190	56,304	57,226
Shares used to compute loss per share - Diluted (in shares)	56,505	57,336	56,399	57,349
Service
Revenues:
Total revenues	$ 696,779	$ 610,940	$ 1,316,498	$ 1,171,154
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	473,423	412,356	921,072	803,443
Product
Revenues:
Total revenues	152,361	141,848	282,420	270,575
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 110,161	$ 107,447	$ 208,937	$ 212,945