Derivative Instruments - Designated as hedging, Financial Performance (Details) (Interest Rate Swap [Member], Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Interest Expense [Member]	Jun. 30, 2012 Interest Expense [Member]	Jun. 30, 2013 Interest Expense [Member]	Jun. 30, 2012 Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 3,780	$ (760)
Amount of Loss Reclassified from AOCI into Earnings			$ (310)	$ (110)	$ (320)	$ (110)