Derivative Instruments and Hedging Activities (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	$ 925,341,000
Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	479,200,000	479,200,000
Asset Derivatives, Fair Value	7,811,000	6,493,000
Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	405,028,000	306,932,000
Asset Derivatives, Fair Value	4,383,000	1,869,000
Accounts Payable and Accrued Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	886,939,000	1,086,939,000
Liability Derivatives, Fair Value	84,313,000	87,264,000
Accounts Payable and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	38,402,000	38,425,000
Liability Derivatives, Fair Value	14,895,000	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	25,000	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	2,000	12,000
Interest rate caps [Member] | Accounts Payable 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 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	0	0
Asset Derivatives, Fair Value	0	0
Interest rate swaps [Member] | Accounts Payable 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	72,331,000	75,281,000
TROR [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	256,187,000
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	7,786,000	6,379,000
TROR [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Asset Derivatives, Current Notional	101,338,000	101,410,000
Asset Derivatives, Fair Value	4,381,000	1,857,000
TROR [Member] | Accounts Payable and Accrued Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	217,785,000	217,785,000
Liability Derivatives, Fair Value	11,982,000	11,983,000
TROR [Member] | Accounts Payable and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Liability Derivatives, Current Notional	38,402,000	38,425,000
Liability Derivatives, Fair Value	$ 14,895,000	$ 15,098,000