Derivative Instruments - Designated as hedging, Financial Performance (Details) (Interest Rate Swap [Member], Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Interest Expense [Member]	Mar. 31, 2012 Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in AOCI on Derivative (Effective Portion, net of tax)	$ (170)	$ (760)
Amount of Loss Reclassified from AOCI into Earnings			$ (10)	$ 0