Derivative Instruments And Hedging Activities Interest Rate Cap Agreements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Premium payments on interest rate cap agreements	$ 0.3	$ 3.7	$ 5.9
Interest Rate Cap [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Purchased	6	4	4
Interest Rate Cap Purchased During 2012 [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	650.0
Premium payments on interest rate cap agreements	0.3
Derivative, Cap Interest Rate	1.50%
Interest Rate Cap Purchased During 2011 [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments		500.0
Premium payments on interest rate cap agreements		3.7
Derivative, Cap Interest Rate	3.50%
Interest Rate Cap Purchased During 2010 [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments			1,100.0
Premium payments on interest rate cap agreements			$ 5.9
Derivative, Cap Interest Rate	3.50%