Risk Management and Use of Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ 464	$ 331	$ 851	$ 666
Interest rate swap
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)	441	331	875	666
Foreign currency contracts
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ 23		$ (24)