CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Service revenues									$ 2,398,650	$ 2,280,809	$ 2,744,272
Product revenues									546,328	474,417	530,865
Total revenues	$ 747,403	$ 755,846	$ 752,788	$ 688,941	$ 692,113	$ 729,520	$ 697,510	$ 636,083	2,944,978	2,755,226	3,275,137
Cost of revenues: (exclusive of items shown separately below)
Service revenues									1,641,798	1,543,210	1,898,907
Product revenues									420,875	389,647	457,899
Total cost of revenues	526,690	519,595	519,803	496,585	496,661	491,915	480,002	464,279	2,062,673	1,932,857	2,356,806
Selling, general and administrative expenses									456,648	422,015	414,164
Accretion of environmental liabilities									9,460	10,177	10,402
Depreciation and amortization									288,422	287,002	274,194
Goodwill impairment charges						34,000			0	34,013	31,992
Income (loss) from operations	27,935	47,663	46,744	5,433	21,943	16,802	34,504	(4,087)	127,775	69,162	187,579
Other (expense) income, net	(3,305)	(432)	(833)	(1,549)	6,932	(198)	(189)	(350)	(6,119)	6,195	(1,380)
Loss on early extinguishment of debt		(1,900)	(6,000)						(7,891)	0	0
Gain on sale of businesses			31,700			16,400			30,732	16,884	0
Interest expense, net of interest income of $1,897, $784, and $626, respectively									(85,808)	(83,525)	(76,553)
Income (loss) before (benefit) provision for income taxes									58,689	8,716	109,646
(Benefit) provision for income taxes									(42,050)	48,589	65,544
Net income (loss)	$ 84,194	$ 12,058	$ 25,880	$ (21,393)	$ (12,713)	$ (10,255)	$ 3,966	$ (20,871)	$ 100,739	$ (39,873)	$ 44,102
Earnings (loss) per share:
Basic (in dollars per share)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ (0.22)	$ (0.18)	$ 0.07	$ (0.36)	$ 1.77	$ (0.69)	$ 0.76
Diluted (in dollars per share)	$ 1.48	$ 0.21	$ 0.45	$ (0.37)	$ (0.22)	$ (0.18)	$ 0.07	$ (0.36)	$ 1.76	$ (0.69)	$ 0.76
Shares used to compute earnings (loss) per share — Basic (in shares)									57,072	57,532	58,324
Shares used to compute earnings (loss) per share — Diluted (in shares)									57,200	57,532	58,434