QUARTERLY DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
QUARTERLY DATA (UNAUDITED) [Abstract]
Revenues	$ 545,886		$ 556,053		$ 447,235		$ 434,962		$ 417,058		$ 487,651		$ 471,639		$ 354,896		$ 1,984,136	$ 1,731,244	$ 1,074,220
Cost of revenues (exclusive of items shown separately below)	373,142	[1]	386,518	[1]	307,754	[1]	312,577	[1]	290,770	[1]	335,273	[1]	324,280	[1]	260,417	[1]	1,379,991	1,210,740	753,483
Gross Profit	172,744		169,535		139,481		122,385		126,288		152,378		147,359		94,479
Income from operations	59,247		66,792		51,884		39,742		42,998		73,372		71,923		23,619		217,665	211,912	82,065
Other income (expense)	471		164		2,868		2,899		310		(669)		2,708		446		6,402	2,795	259
Income from discontinued operations, net of tax									0		0		2,412		382		0	2,794	1,439
Net income	$ 38,233		$ 37,133		$ 29,156		$ 22,730		$ 23,329		$ 38,827		$ 57,929		$ 10,430		$ 127,252	$ 130,515	$ 36,686
Basic income per share (in dollars per share)	$ 0.72		$ 0.70		$ 0.55		$ 0.43		$ 0.44		$ 0.74		$ 1.1		$ 0.2		$ 2.40	$ 2.48	$ 0.74
Diluted income per share (in dollars per share)	$ 0.72		$ 0.70		$ 0.55		$ 0.43		$ 0.44		$ 0.73		$ 1.1		$ 0.2		$ 2.39	$ 2.47	$ 0.74

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