Risk Management and Use of Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	$ (1,573)	$ 3,094	$ (4,024)	$ 13,412
Interest rate cap | Cash Flow Hedging
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	355	298	687	565
Interest rate swap | Cash Flow Hedging
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	(2,502)	6,490	(4,421)	8,457
Foreign currency collars | Cash Flow Hedging
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	(83)	(1,077)	(199)	(61)
Foreign currency forward | Cash Flow Hedging
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	400	(1,770)	(409)	3,435
Foreign currency forward | Net Investment Hedging
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	257	(847)	318	1,016
Noncontrolling interest | Interest rate cap
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	$ 200	$ 100	$ 300	$ 300