UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Total revenues	$ 868,678	$ 849,140	$ 1,649,517	$ 1,598,918
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	594,933	583,584	1,159,297	1,130,009
Selling, general and administrative expenses	123,920	125,995	238,732	241,083
Accretion of environmental liabilities	2,560	2,448	5,134	4,878
Depreciation and amortization	74,217	72,760	149,572	147,604
Income from operations	73,048	64,353	96,782	75,344
Other (expense) income, net	(564)	846	2,419	547
Interest expense, net of interest income of $903, $587, $1,829 and $1,350, respectively	(20,215)	(20,769)	(39,979)	(41,039)
Income before provision for income taxes	52,269	44,430	59,222	34,852
Provision for income taxes	16,025	13,683	22,002	16,736
Net income	$ 36,244	$ 30,747	$ 37,220	$ 18,116
Earnings per share:
Basic (in USD per share)	$ 0.65	$ 0.55	$ 0.67	$ 0.32
Diluted (in USD per share)	$ 0.65	$ 0.54	$ 0.66	$ 0.32
Shares used to compute earnings per share - Basic (in shares)	55,875	56,410	55,861	56,304
Shares used to compute earnings per share - Diluted (in shares)	56,066	56,505	56,001	56,399
Service
Revenues:
Total revenues	$ 715,085	$ 696,779	$ 1,371,743	$ 1,316,498
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	480,229	473,423	943,712	921,072
Product
Revenues:
Total revenues	153,593	152,361	277,774	282,420
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 114,704	$ 110,161	$ 215,585	$ 208,937