Risk Management and Use of Derivative Financial Instruments - Derivative Gain Loss Reclassified From OCI (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Derivatives, income (loss) reclassified from AOCI to Income, effective portion, net	$ 988	$ 558	$ 2,044	$ 2,710
Foreign currency forward contracts | Other gains and (losses)
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Derivatives, income (loss) reclassified from AOCI to Income, effective portion, net	1,315	1,161	2,807	4,019
Interest rate swaps | Interest expense
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Derivatives, income (loss) reclassified from AOCI to Income, effective portion, net	(313)	(603)	(744)	(1,309)
Interest rate caps | Interest expense
Amount of Gain (Loss) Reclassified from Other Comprehensive Income into Income (Effective Portion)
Derivatives, income (loss) reclassified from AOCI to Income, effective portion, net	$ (14)	$ 0	$ (19)	$ 0