Risk Management and Use of Derivative Financial Instruments - Derivative Gain Loss Recognized in OCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	$ 775	$ (2,319)	$ 3,488	$ (6,740)
Derivatives in Cash Flow Hedging Relationships | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	523	42	2,043	12
Derivatives in Cash Flow Hedging Relationships | Foreign currency collars
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	431	(1,376)	1,852	(3,990)
Derivatives in Cash Flow Hedging Relationships | Foreign currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	(186)	(819)	(388)	(2,452)
Derivatives in Cash Flow Hedging Relationships | Interest rate caps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	4	8	24	4
Net Investment Hedging | Foreign currency collars
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	3	(87)	(43)	(55)
Net Investment Hedging | Foreign currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized on Derivatives in Other Comprehensive (Loss) Income (Effective Portion)	$ 0	$ (87)	$ 0	$ (259)