Risk Management and Use of Derivative Financial Instruments - Derivative Gain Loss Reclassified From OCI (Details) - Derivatives in Cash Flow Hedging Relationships - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ (46)	$ 232
Foreign currency forward contracts | Other gains and (losses)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)	222	356
Foreign currency collars | Other gains and (losses)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)	(154)	92
Interest rate swaps | Interest expense
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)	(83)	(211)
Interest rate caps | Interest expense
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income into Income (Effective Portion)	$ (31)	$ (5)