Derivative Instruments Derivative Instruments Affecting the Consolidated Statements of Income (Details) (Designated as Hedging Instrument [Member], Cash Flow Hedging [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in OCI on Derivative (Effective Portion)	$ (1.6)	$ 0	$ (0.7)
Amount of Gain/(Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(0.7)	(0.4)	(5.1)
Amount of Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from EffectivenessTesting)	0	0	0
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Recognized in OCI on Derivative (Effective Portion)	(1.6)	0	(0.7)
Interest Rate Swaps [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain/(Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (0.7)	$ (0.4)	$ (5.1)