Derivative Instruments and Hedging Activities (Details) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	$ 1,030,318,000
Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	544,762,000	$ 479,200,000
Asset Derivatives, Fair Value	8,072,000	6,493,000
Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	404,954,000	306,932,000
Asset Derivatives, Fair Value	4,681,000	1,869,000
Accounts Payable, Accrued Expenses and Accrued Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	991,939,000	1,086,939,000
Liability Derivatives, Fair Value	74,747,000	87,264,000
Accounts Payable, Accrued Expenses and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	38,379,000	38,425,000
Liability Derivatives, Fair Value	12,303,000	15,098,000
Interest rate caps [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	330,000,000	330,000,000
Asset Derivatives, Fair Value	6,000	114,000
Interest rate caps [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	303,690,000	205,522,000
Asset Derivatives, Fair Value	0	12,000
Interest rate caps [Member] | Accounts Payable, Accrued Expenses and Accrued Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	0	0
Liability Derivatives, Fair Value	0	0
Interest rate caps [Member] | Accounts Payable, Accrued Expenses and Accrued 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 swaps [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	65,562,000	0
Asset Derivatives, Fair Value	935,000	0
Interest rate swaps [Member] | Accounts Payable, Accrued Expenses and Accrued Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	669,154,000	869,154,000
Liability Derivatives, Fair Value	64,463,000	75,281,000
TROR [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	361,164,000
TROR [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	149,200,000	149,200,000
Asset Derivatives, Fair Value	7,131,000	6,379,000
TROR [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	101,264,000	101,410,000
Asset Derivatives, Fair Value	4,681,000	1,857,000
TROR [Member] | Accounts Payable, Accrued Expenses and Accrued Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	322,785,000	217,785,000
Liability Derivatives, Fair Value	10,284,000	11,983,000
TROR [Member] | Accounts Payable, Accrued Expenses and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	38,379,000	38,425,000
Liability Derivatives, Fair Value	$ 12,303,000	$ 15,098,000