Risk Management and Use of Derivative Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (236)	$ (132)
Foreign currency collars
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	417	618
Foreign currency forward
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	288	138
Interest rate cap
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(267)	(182)
Interest rate swap
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (674)	$ (706)