QUARTERLY DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 845,024		$ 851,465		$ 858,480		$ 846,667		$ 879,430		$ 907,535		$ 860,528		$ 862,163		$ 3,401,636	$ 3,509,656	$ 2,187,908
Cost of revenues	610,720	[1]	598,407	[1]	606,950	[1]	625,719	[1]	645,164	[1]	647,119	[1]	614,326	[1]	636,024	[1]	2,441,796	2,542,633	1,540,621
Gross profit	234,304		253,058		251,530		220,948		234,266		260,416		246,202		226,139
Income (loss) from operations	57,537		(42,748)		67,115		29,906		58,877		73,608		53,243		34,828		111,810	220,556	202,204
Other income (expense)	244		613		(655)		4,178		(325)		(150)		1,655		525		4,380	1,705	(802)
Net (loss) income	27,377		(93,337)		28,672		8,960		26,801		35,361		22,902		10,502		(28,328)	95,566	129,674
Basic income per share (in dollars per share)	$ 0.46	[2]	$ (1.55)	[2]	$ 0.47	[2]	$ 0.15	[2]	$ 0.44	[2]	$ 0.58	[2]	$ 0.38	[2]	$ 0.17	[2]	$ (0.47)	$ 1.58	$ 2.41
Diluted income per share (in dollars per share)	$ 0.46	[2]	$ (1.55)	[2]	$ 0.47	[2]	$ 0.15	[2]	$ 0.44	[2]	$ 0.58	[2]	$ 0.38	[2]	$ 0.17	[2]	$ (0.47)	$ 1.57	$ 2.40
Unrecognized tax benefits	$ 2,537		$ 5,400						$ 1,304								$ 2,537	$ 1,304	$ 3,543	$ 36,217

[1] (1)Items shown separately on the statements of income consist of (i) accretion of environmental liabilities and (ii) depreciation and amortization.

[2] (2)Earnings per share are computed independently for each of the quarters presented. Accordingly, the quarterly basic and diluted earnings per share may not equal the total computed for the year. (3)In the fourth quarter of 2014 an adjustment was recorded to correct income tax expense that was recorded in the third quarter of 2014 resulting in a benefit of approximately $5.4 million in the fourth quarter.