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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)	$ 225	$ 78	$ 457	$ 238
Foreign currency forward contracts | Other income and (expenses)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)	334	296	690	629
Interest rate swaps | Interest expense
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)	(176)	(217)	(387)	(429)
Foreign currency collars | Other income and (expenses)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)	77	0	169	39
Interest rate caps | Interest expense
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)
Amount of Gain (Loss) on Derivatives Reclassified from Other Comprehensive Income (Loss) into Income (Effective Portion)	$ (10)	$ (1)	$ (15)	$ (1)