Risk Management and Use of Derivative Financial Instruments (Details 2) (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) Recognized in Other Comprehensive Income (Loss) Activity
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives (Effective Portion)	$ (2,867)	$ 3,073
Interest rate swap
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives (Effective Portion)	(186)	828
Interest rate cap
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives (Effective Portion)	(17)	(3)
Foreign currency contracts
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives (Effective Portion)	$ (2,664)	$ 2,248