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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 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)	$ (1,886)	$ 1,768	$ (4,753)	$ 4,841
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)	(1,431)	2,825	(1,617)	3,653
Interest rate caps
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Amount of Gain (Loss) Recognized in Other Comprehensive Income on Derivatives (Effective Portion)	(4)	13	(21)	10
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)	$ (451)	$ (1,070)	$ (3,115)	$ 1,178