Derivative Instruments - Designated as hedging, Financial Performance Narrative (Details) (Interest Rate Swap [Member], Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss Reclassification from AOCI into Earnings, Estimate of Time to Transfer	12 months
Amount of Loss expected to be reclassified from AOCI into Earnings	$ 0.6