Risk Management and Use of Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivatives, gain (loss) reclassified from AOCI to Income, effective portion, net	$ (2,365)	$ (1,440)	$ (4,525)	$ (2,634)
Interest rate cap
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivatives, gain (loss) reclassified from AOCI to Income, effective portion, net	(355)	(298)	(687)	(565)
Interest rate swap
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivatives, gain (loss) reclassified from AOCI to Income, effective portion, net	(2,217)	(1,748)	(3,932)	(3,382)
Foreign currency collars
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivatives, gain (loss) reclassified from AOCI to Income, effective portion, net	118	523	194	941
Foreign currency forward
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivatives, gain (loss) reclassified from AOCI to Income, effective portion, net	$ 89	$ 83	$ (100)	$ 372