Risk Management and Use of Derivative Financial Instruments (Narratives) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Risk Management and Use of Deriviative Financial Instruments
Total credit exposure on derivatives	$ 9,900,000
Total credit exposure on derivatives to a single counterparty	6,500,000
Derivative Instrument Detail
Amounts attributable to noncontrolling interests	100,000	100,000
Derivative liability, fair value	(19,200,000)		(23,000,000)
Loss on contract termination	20,800,000		25,100,000
Derivative, notional, noncontrolling interest	53,300,000
Foreign currency exchange rate	1.2821		1.3218
Interest rate swap
Derivative Instrument Detail
Estimated amount reclassified from OCI to income, derivatives	7,600,000
Derivative Instruments Gain Loss Reclassification From Accumulated OCI To Interest Expense Noncontrolling Interest	600,000
Foreign currency contract
Derivative Instrument Detail
Estimated amount reclassified from OCI to income, derivatives	3,500,000
Interest rate cap
Derivative Instrument Detail
Debt, interest rate at period end	2.80%
Cap rate	4.00%
Embedded derivatives
Derivative Instrument Detail
Foreign currency exchange rate	1.278
Maximum
Derivative Instrument Detail
Derivative, fair value, noncontrolling interest	$ 100,000