Long-term Debt and Derivatives (Details 2) (USD $)	3 Months Ended	9 Months Ended					3 Months Ended		3 Months Ended		3 Months Ended	1 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Revolving credit facility Issuance of debt	Jul. 14, 2011 Revolving credit facility Issuance of debt	Sep. 30, 2011 Variable rate Term Loan A	Jul. 14, 2011 Variable rate Term Loan A Issuance of debt	Sep. 30, 2011 Variable rate Term Loan B	Jul. 14, 2011 Variable rate Term Loan B Issuance of debt	Sep. 30, 2011 Previous senior secured credit facility	Jul. 31, 2011 Issuance of debt loan	Sep. 30, 2011 Issuance of debt	Jul. 14, 2011 Issuance of debt
Future minimum repayments of long-term debt
Within one year	$ 45,581,000	$ 45,581,000
1-3 years	111,435,000	111,435,000
3-5 years	775,215,000	775,215,000
Over 5 years	1,037,352,000	1,037,352,000
Total minimum payments	1,969,583,000	1,969,583,000		2,171,123,000
Letters of credit outstanding	25,000,000	25,000,000
Available borrowing capacity	475,000,000	475,000,000
Long-term Debt
Variable rate term loan						700,000,000		700,000,000		750,000,000
Maximum borrowing capacity	2,150,000,000	2,150,000,000											1,639,400,000	2,150,000,000
Revolving credit facility amount outstanding					200,000,000
Term loan amount outstanding								691,300,000		748,100,000
Interest rate, description							LIBOR		LIBOR
Interest rate added to the base rate (as a percent)							1.50%		2.75%
Interest rate description floor rate (as a percent)									1.00%
Number of term loans												2
Loss on early extinguishment of debt	$ (17,838,000)	$ (17,838,000)	$ (519,000)								$ 10,200,000