Derivative Instruments and Hedging Activities (Details 3)	9 Months Ended
	Sep. 30, 2015 USD ($)
Derivative [Line Items]
Notional Amount	$ 1,095,638,000
Fair Value Prior to Nonperformance Risk	87,979,000
Nonperformance Risk	(2,401,000)
Collateral Posted	50,569,000
Property Specific Swap [Member]
Derivative [Line Items]
Notional Amount	734,497,000
Fair Value Prior to Nonperformance Risk	63,553,000
Nonperformance Risk	(2,457,000)
Collateral Posted	$ 0
Nature of Collateral	Mortgage liens
Credit Risk Contingent Feature	None
TROR [Member]
Derivative [Line Items]
Notional Amount	$ 361,141,000
Fair Value Prior to Nonperformance Risk	24,426,000
Nonperformance Risk	56,000
Collateral Posted	$ 50,569,000
Nature of Collateral	Restricted cash, notes receivable, letters of credit
Credit Risk Contingent Feature	None