Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities (Details 3) (USD $)	9 Months Ended
	Sep. 30, 2014
Derivative [Line Items]
Notional Amount	$ 1,137,767,000
Fair Value Prior to Nonperformance Risk	110,952,000
Nonperformance Risk	(4,263,000)
Collateral Posted	52,185,000
Property Specific Swap [Member]
Derivative [Line Items]
Notional Amount	670,995,000
Fair Value Prior to Nonperformance Risk	83,580,000
Nonperformance Risk	(4,340,000)
Collateral Posted	0
Nature of Collateral	Mortgage liens
Credit Risk Contingent Feature	None
Total Return Swap [Member]
Derivative [Line Items]
Notional Amount	266,772,000
Fair Value Prior to Nonperformance Risk	27,206,000
Nonperformance Risk	77,000
Collateral Posted	52,015,000
Nature of Collateral	Restricted cash, securities, notes receivable, letters of credit
Credit Risk Contingent Feature	None
Corporate Aggregate Swap [Member]
Derivative [Line Items]
Notional Amount	200,000,000
Fair Value Prior to Nonperformance Risk	166,000
Nonperformance Risk	0
Collateral Posted	$ 170,000
Nature of Collateral	Restricted cash
Credit Risk Contingent Feature	Credit rating