Derivative Instruments and Hedging Activities (Details) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2012	Jan. 31, 2012
Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	$ 28,100	$ 27,197
Derivative Asset, Fair Value, Gross Asset	791	774
Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	595,217	596,425
Derivative Asset, Fair Value, Gross Asset	13,620	10,630
Accounts Payable and Accrued Expenses [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	1,142,155	1,140,753
Derivative Liability, Fair Value, Gross Liability	151,261	158,653
Accounts Payable and Accrued Expenses [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	30,360	30,360
Derivative Liability, Fair Value, Gross Liability	14,239	15,367
Total Return Swap [Member] | Other Assets [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	28,100	27,197
Derivative Asset, Fair Value, Gross Asset	791	774
Total Return Swap [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	140,800	141,703
Derivative Asset, Fair Value, Gross Asset	12,709	9,534
Total Return Swap [Member] | Accounts Payable and Accrued Expenses [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	243,560	243,560
Derivative Liability, Fair Value, Gross Liability	10,116	9,954
Total Return Swap [Member] | Accounts Payable and Accrued Expenses [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	30,360	30,360
Derivative Liability, Fair Value, Gross Liability	14,239	15,367
Interest rate swap agreements [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	19,521	19,521
Derivative Asset, Fair Value, Gross Asset	894	1,083
Interest rate swap agreements [Member] | Accounts Payable and Accrued Expenses [Member] | Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Derivative Liability, Notional Amount	898,595	897,193
Derivative Liability, Fair Value, Gross Liability	141,145	148,699
Interest rate caps [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Fair Value of Derivative Instruments
Current Notional Derivatives Asset	434,896	435,201
Derivative Asset, Fair Value, Gross Asset	$ 17	$ 13