Risk Management and Use of Derivative Financial Instruments - Derivative Gain Loss Recognized in OCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	$ (808)	$ (486)
Derivatives in Cash Flow Hedging Relationships | Foreign currency collars
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	(1,205)	(235)
Derivatives in Cash Flow Hedging Relationships | Interest rate swaps
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	1,157	247
Derivatives in Cash Flow Hedging Relationships | Foreign currency forward contracts
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	(629)	(471)
Derivatives in Cash Flow Hedging Relationships | Interest rate caps
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	18	2
Net Investment Hedging | Foreign currency collars
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	(126)	(10)
Net Investment Hedging | Foreign currency forward contracts
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)	$ (23)	$ (19)