Derivative Instruments and Hedging Activities (Details 2) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2011	Jul. 31, 2010
Derivatives not designated as hedging instruments
Net Gain (Loss) Derivatives Not Designated as Hedging Instruments	$ 213	$ (8,465)	$ 1,057	$ (9,080)
Derivatives designated as fair value hedging instruments
Net Gain (Loss) Recognized Derivatives Designated as Fair Value Hedging Instruments	(5,982)	(3,573)	(7,464)	(5,872)
Total Return Swap [Member]
Derivatives not designated as hedging instruments
Net Gain (Loss) Derivatives Not Designated as Hedging Instruments	414	(3,939)	1,454	(3,778)
Derivatives designated as fair value hedging instruments
Net Gain (Loss) Recognized Derivatives Designated as Fair Value Hedging Instruments	5,982	3,573	7,464	5,872
Interest rate caps, interest rate swaps and floors [Member]
Derivatives not designated as hedging instruments
Net Gain (Loss) Derivatives Not Designated as Hedging Instruments	$ (201)	$ (4,526)	$ (397)	$ (5,302)