Risk Management and Use of Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 23,395	$ (506)	$ (2,262)
Interest rate swap | Derivatives in Cash Flow Hedging Relationships
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(2,628)	4,720	(1,059)
Interest rate cap | Derivatives in Cash Flow Hedging Relationships
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	290	(15)	277
Foreign currency contracts | Derivatives in Cash Flow Hedging Relationships
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	23,167	(5,211)	(1,480)
Foreign currency contracts | Derivatives in Net Investment Hedging Relationships
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	2,566	0	0
Equity method investments | Derivatives in Cash Flow Hedging Relationships
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss) Activity
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 300	$ 500	$ (100)