Risk Management and Use of Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	$ 831	$ (16,758)	$ (5,219)
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	1,188	811	(244)
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	10,107	(11,046)	(6,864)
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	(2,059)	(2,951)	6,698
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	(6,168)	(3,030)	0
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	(2,237)	(734)	(4,809)
Put option | Cash Flow Hedging
Amount of Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)
Derivatives, gain (loss) recognized in OCI, effective portion, net	$ 0	$ 192	$ 0