Risk Management and Use of Derivative Financial Instruments (Details 3) (Derivatives in Cash Flow Hedging Relationships, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ (1,085)	$ (387)
Interest rate swap
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)	(701)	(434)
Foreign currency contracts
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ (384)	$ 47