Derivative Instruments and Hedging Activities (Details) (USD $) In Thousands	Jul. 31, 2011	Jan. 31, 2011
Interest rate caps [Member] | Other Assets [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	$ 105,882	$ 476,100
Fair value of Derivatives Designated as Hedging Instruments, Asset	1	184
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	1,311,593
Fair value of Derivatives Not Designated as Hedging Instruments, Assets	39
Interest rate caps [Member] | Accounts Payable and Accrued Expenses [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	0	0
Fair value of Derivatives Designated as Hedging Instruments, Liability	0	0
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	0
Fair value of Derivatives Not Designated as Hedging Instruments, Liability	0
Interest rate caps and floors [Member] | Other Assets [Member]
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments		1,943,202
Fair value of Derivatives Not Designated as Hedging Instruments, Assets		11
Interest rate caps and floors [Member] | Accounts Payable and Accrued Expenses [Member]
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments		0
Fair value of Derivatives Not Designated as Hedging Instruments, Liability		0
Interest rate swap agreements [Member] | Other Assets [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	0	300,000
Fair value of Derivatives Designated as Hedging Instruments, Asset	0	716
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	20,117	20,117
Fair value of Derivatives Not Designated as Hedging Instruments, Assets	1,523	1,801
Interest rate swap agreements [Member] | Accounts Payable and Accrued Expenses [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	1,196,149	1,285,000
Fair value of Derivatives Designated as Hedging Instruments, Liability	128,547	110,398
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	0	60,900
Fair value of Derivatives Not Designated as Hedging Instruments, Liability	0	14,011
Total Return Swap [Member] | Other Assets [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	9,130	0
Fair value of Derivatives Designated as Hedging Instruments, Asset	15	0
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	140,800	140,800
Fair value of Derivatives Not Designated as Hedging Instruments, Assets	3,824	2,144
Total Return Swap [Member] | Accounts Payable and Accrued Expenses [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	251,852	280,885
Fair value of Derivatives Designated as Hedging Instruments, Liability	13,586	21,938
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	30,600	30,600
Fair value of Derivatives Not Designated as Hedging Instruments, Liability	10,466	10,240
Other Assets [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	115,012	776,100
Fair value of Derivatives Designated as Hedging Instruments, Asset	16	900
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	1,472,510	2,104,119
Fair value of Derivatives Not Designated as Hedging Instruments, Assets	5,386	3,956
Accounts Payable and Accrued Expenses [Member]
Derivatives Designated as Hedging Instruments
Current Notional Derivatives Designated as Hedging Instruments	1,448,001	1,565,885
Fair value of Derivatives Designated as Hedging Instruments, Liability	142,133	132,336
Derivatives Not Designated as Hedging Instruments
Current Notional Derivatives not Designated as Hedging Instruments	30,600	91,500
Fair value of Derivatives Not Designated as Hedging Instruments, Liability	$ 10,466	$ 24,251