Risk Management and Use of Derivative Financial Instruments - Derivative Gain Loss Recognized in OCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	$ (3,935)	$ 171	$ (4,421)	$ (3,890)
Derivatives in Cash Flow Hedging Relationships | Foreign currency collars
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	(2,379)	651	(2,613)	(432)
Derivatives in Cash Flow Hedging Relationships | Foreign currency forward contracts
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	(1,162)	279	(1,634)	(989)
Derivatives in Cash Flow Hedging Relationships | Interest rate swaps
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	(277)	(832)	(32)	(2,313)
Derivatives in Cash Flow Hedging Relationships | Interest rate caps
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	(6)	(3)	(2)	(16)
Net Investment Hedging | Foreign currency collars
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	(23)	7	(33)	(8)
Net Investment Hedging | Foreign currency forward contracts
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Loss) (Effective Portion)	$ (88)	$ 69	$ (107)	$ (132)