Derivative Instruments and Hedging Activities (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	$ 460,970,000	$ 18,970,000
Asset Derivatives, Fair Value	5,315,000	903,000
Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	293,327,000	447,532,000
Asset Derivatives, Fair Value	332,000	155,000
Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	1,098,904,000	1,301,144,000
Liability Derivatives, Fair Value	100,463,000	107,630,000
Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	39,009,000	39,052,000
Liability Derivatives, Fair Value	15,076,000	15,477,000
Interest rate caps [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	330,000,000
Asset Derivatives, Fair Value	156,000
Interest rate caps [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	266,775,000	447,532,000
Asset Derivatives, Fair Value	58,000	155,000
Interest rate caps [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	0
Liability Derivatives, Fair Value	0
Interest rate caps [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	0	0
Liability Derivatives, Fair Value	0	0
Interest rate swap agreements [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	0	0
Asset Derivatives, Fair Value	0	0
Interest rate swap agreements [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	871,119,000	961,359,000
Liability Derivatives, Fair Value	88,646,000	97,858,000
Total Return Swap [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	130,970,000	18,970,000
Asset Derivatives, Fair Value	5,159,000	903,000
Total Return Swap [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	26,552,000	0
Asset Derivatives, Fair Value	274,000	0
Total Return Swap [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	227,785,000	339,785,000
Liability Derivatives, Fair Value	11,817,000	9,772,000
Total Return Swap [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	39,009,000	39,052,000
Liability Derivatives, Fair Value	$ 15,076,000	$ 15,477,000