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)
Derivatives, income (loss) recognized in OCI, effective portion, net	$ (2,815)	$ (3,364)
Equity Method Investments
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	500	500
Derivatives in Cash Flow Hedging Relationships | Foreign currency forward contracts
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	(4,224)	(3,749)
Derivatives in Cash Flow Hedging Relationships | Interest rate swaps
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	2,022	993
Derivatives in Cash Flow Hedging Relationships | Foreign currency collars
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	(556)	(57)
Derivatives in Cash Flow Hedging Relationships | Interest rate caps
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	(23)	(258)
Derivatives in Net Investment Hedging Relationships | Foreign currency forward contracts
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	(22)	(291)
Derivatives in Net Investment Hedging Relationships | Foreign currency collars
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive Income (Effective Portion)
Derivatives, income (loss) recognized in OCI, effective portion, net	$ (12)	$ (2)