QUARTERLY DATA (UNAUDITED) (Details) (USD $)	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly [Line Items]
Revenues	$ 558,962,000		$ 533,806,000		$ 523,118,000		$ 572,022,000		$ 545,886,000		$ 556,053,000		$ 447,235,000		$ 434,962,000		$ 2,187,908,000	$ 1,984,136,000	$ 1,731,244,000
Cost of revenues (exclusive of items shown separately below)	399,743,000	[1]	372,940,000	[1]	367,623,000	[1]	400,315,000	[1]	373,142,000	[2]	386,518,000	[2]	307,754,000	[2]	312,577,000	[2]	1,540,621,000	1,379,991,000	1,210,740,000
Gross Profit	159,219,000		160,866,000		155,495,000		171,707,000		172,744,000		169,535,000		139,481,000		122,385,000
Income from operations	36,231,000		56,739,000		47,533,000		61,701,000		59,247,000		66,792,000		51,884,000		39,742,000		202,204,000	217,665,000	211,912,000
Other (expense) income	(337,000)		(91,000)		(75,000)		(299,000)		471,000		164,000		2,868,000		2,899,000		(802,000)	6,402,000	2,795,000
Net income	61,874,000		12,359,000		23,426,000		32,015,000		38,233,000		37,133,000		29,156,000		22,730,000		129,674,000	127,252,000	130,515,000
Basic income per share (in dollars per share)	$ 1.11		$ 0.23		$ 0.44		$ 0.6		$ 0.72		$ 0.70		$ 0.55		$ 0.43		$ 2.41	$ 2.40	$ 2.48
Loss on early extinguishment of debt																	(26,385,000)	0	(2,294,000)
Diluted income per share (in dollars per share)	$ 1.11		$ 0.23		$ 0.44		$ 0.6		$ 0.72		$ 0.70		$ 0.55		$ 0.43		$ 2.40	$ 2.39	$ 2.47
Change in Tax Benefits [Member]
Quarterly [Line Items]
Unrecognized Tax Benefits, Period Increase (Decrease)																	52,400,000
Secured Senior Notes 2016 | Senior Notes [Member]
Quarterly [Line Items]
Long-term Debt, Gross	$ 0								$ 520,000,000								$ 0	$ 520,000,000

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

[2] The third quarter net income and earnings per share were impacted by a $26.4 million loss on early extinguishment of debt in connection with a redemption and repurchase of our $520.0 million previously outstanding senior secured notes. The fourth quarter 2012 net income and earnings per share were impacted by a decrease in unrecognized tax benefits of $52.4 million resulting from expiring statute of limitation periods related to an historical Canadian debt restructuring transaction.