Derivative Instruments and Hedging Activities (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Not Designated as Hedging Instrument [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	$ 1,227	$ (817)	$ (1,485)
Total Return Swap [Member] | Fair Value Hedging [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	11,855	1,924	16,351
Total Return Swap [Member] | Not Designated as Hedging Instrument [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	2,264	1,341	(2,873)
Interest rate caps, interest rate swaps and floors [Member] | Not Designated as Hedging Instrument [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	$ (1,037)	$ (2,158)	$ 1,388