Derivative Instruments - Designated as hedging, Financial Performance (Details) (Interest Rate Swap [Member], Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in AOCI on Derivative (Effective Portion, net of tax)	$ (760)	$ 0
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Reclassified from AOCI into Earnings	$ (250)	$ (360)	$ (2,350)