Derivative Instruments and Hedging Activities (Details) (USD $) In Thousands, unless otherwise specified	Oct. 31, 2011	Jan. 31, 2011
Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	$ 27,197	$ 776,100
Derivative Asset, Fair Value, Gross Asset	414	900
Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	1,435,088	2,104,119
Derivative Asset, Fair Value, Gross Asset	6,863	3,956
Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	1,431,105	1,565,885
Derivative Liability, Fair Value, Gross Liability	152,260	132,336
Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	30,360	91,500
Derivative Liability, Fair Value, Gross Liability	13,728	24,251
Total Return Swap [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	27,197	0
Derivative Asset, Fair Value, Gross Asset	414	0
Total Return Swap [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	141,703	140,800
Derivative Asset, Fair Value, Gross Asset	5,507	2,144
Total Return Swap [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	233,785	280,885
Derivative Liability, Fair Value, Gross Liability	11,795	21,938
Total Return Swap [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	30,360	30,600
Derivative Liability, Fair Value, Gross Liability	13,728	10,240
Interest rate caps and floors [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset		1,943,202
Derivative Asset, Fair Value, Gross Asset		11
Interest rate caps and floors [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount		0
Derivative Liability, Fair Value, Gross Liability		0
Interest rate swap agreements [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	0	300,000
Derivative Asset, Fair Value, Gross Asset	0	716
Interest rate swap agreements [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	20,117	20,117
Derivative Asset, Fair Value, Gross Asset	1,330	1,801
Interest rate swap agreements [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	1,197,320	1,285,000
Derivative Liability, Fair Value, Gross Liability	140,465	110,398
Interest rate swap agreements [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	0	60,900
Derivative Liability, Fair Value, Gross Liability	0	14,011
Interest rate caps [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	0	476,100
Derivative Asset, Fair Value, Gross Asset	0	184
Interest rate caps [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	1,273,268
Derivative Asset, Fair Value, Gross Asset	26
Interest rate caps [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	0	0
Derivative Liability, Fair Value, Gross Liability	0	0
Interest rate caps [Member] | Accounts Payable, Accrued Expenses and Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	0
Derivative Liability, Fair Value, Gross Liability	$ 0