Segment Reporting (Details 3) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Reconciliation of Company's primary measure of segment profitability to Income before income tax provision
Operating income (loss) before depreciation, amortization and gain (loss) on disposal of assets	$ 134,354	$ 113,692	$ 367,061	$ 315,363
Depreciation	(38,868)	(34,441)	(108,843)	(99,349)
Amortization of intangibles	(5,138)	(3,616)	(14,788)	(10,800)
Gain (loss) on disposal of assets	(1,034)	50	(742)	(572)
Interest expense	(12,029)	(9,419)	(31,948)	(30,842)
Interest income	132	135	408	453
Loss on extinguishment of debt				(10,193)
Other income (expense), net	(899)	1,500	(750)	1,970
Income before income tax provision	$ 76,518	$ 67,901	$ 210,398	$ 166,030