UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Total revenues	$ 780,839	$ 749,778
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	564,364	546,425
Selling, general and administrative expenses	114,812	115,088
Accretion of environmental liabilities	2,574	2,430
Depreciation and amortization	75,355	74,844
Income from operations	23,734	10,991
Other income (expense), net	2,983	(299)
Interest expense, net of interest income of $926 and $764, respectively	(19,764)	(20,270)
Income (loss) before provision for income taxes	6,953	(9,578)
Provision for income taxes	5,977	3,053
Net income (loss)	$ 976	$ (12,631)
Earnings (loss) per share:
Basic (in USD per share)	$ 0.02	$ (0.22)
Diluted (in USD per share)	$ 0.02	$ (0.22)
Shares used to compute loss per share - Basic (in shares)	55,848	56,457
Shares used to compute loss per share - Diluted (in shares)	56,082	56,457
Service
Revenues:
Total revenues	$ 656,658	$ 619,719
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	463,483	447,649
Product
Revenues:
Total revenues	124,181	130,059
Cost of revenues: (exclusive of items shown separately below)
Total cost of revenues	$ 100,881	$ 98,776