UNAUDITED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues:
Service revenues	$ 665,275	$ 673,872	$ 1,325,370	$ 1,346,494
Product revenues	193,205	186,656	379,777	376,197
Total revenues	858,480	860,528	1,705,147	1,722,691
Cost of revenues (exclusive of items shown separately below)
Service revenues	445,757	455,603	912,556	923,975
Product revenues	161,193	158,723	320,113	326,375
Total cost of revenues	606,950	614,326	1,232,669	1,250,350
Selling, general and administrative expenses	115,731	122,612	234,693	251,082
Accretion of environmental liabilities	2,609	2,879	5,333	5,714
Depreciation and amortization	66,075	67,468	135,431	127,474
Income from operations	67,115	53,243	97,021	88,071
Other (expense) income	(655)	1,655	3,523	2,180
Interest expense, net of interest income of $211, $155, $416 and $266, respectively	(19,382)	(19,585)	(38,936)	(39,458)
Income before provision for income taxes	47,078	35,313	61,608	50,793
Provision for income taxes	18,406	12,411	23,976	17,389
Net income	$ 28,672	$ 22,902	$ 37,632	$ 33,404
Earnings per share:
Basic (in USD per share)	$ 0.47	$ 0.38	$ 0.62	$ 0.55
Diluted (in USD per share)	$ 0.47	$ 0.38	$ 0.62	$ 0.55
Shares used to compute earnings per share - Basic	60,665	60,550	60,695	60,507
Shares used to compute earnings per share - Diluted	60,778	60,687	60,822	60,658