Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities (Details 3) - Jun. 30, 2015 - USD ($)	Total
Derivative [Line Items]
Notional Amount	$ 1,030,318,000
Fair Value Prior to Nonperformance Risk	89,771,000
Nonperformance Risk	(2,721,000)
Collateral Posted	50,562,000
Property Specific Swap [Member]
Derivative [Line Items]
Notional Amount	669,154,000
Fair Value Prior to Nonperformance Risk	67,249,000
Nonperformance Risk	(2,786,000)
Collateral Posted	$ 0
Nature of Collateral	Mortgage liens
Credit Risk Contingent Feature	None
TROR [Member]
Derivative [Line Items]
Notional Amount	$ 361,164,000
Fair Value Prior to Nonperformance Risk	22,522,000
Nonperformance Risk	65,000
Collateral Posted	$ 50,562,000
Nature of Collateral	Restricted cash, notes receivable, letters of credit
Credit Risk Contingent Feature	None