Derivative Instruments and Hedging Activities (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jul. 31, 2012		Jul. 31, 2011		Jul. 31, 2012		Jul. 31, 2011
Not Designated as Hedging Instrument [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	$ 3,107		$ 213		$ 7,205		$ 1,057
Total Return Swap [Member] | Fair Value Hedging [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	(225)	[1]	5,982	[1]	(370)	[1]	7,464	[1]
Total Return Swap [Member] | Not Designated as Hedging Instrument [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	3,348		414		7,651		1,454
Interest rate caps and interest rate swaps [Member] | Not Designated as Hedging Instrument [Member]
Impact of gains and losses related to derivative instruments
Net Gain (Loss) Recognized Derivatives	$ (241)		$ (201)		$ (446)		$ (397)

[1] The net gain (loss) recognized in interest expense from the change in fair value of the underlying TRS borrowings was $225 and $370 for the three and six months ended July 31, 2012, respectively, and $(5,982) and $(7,464) for the three and six months ended July 31, 2011, respectively, offsetting the gain (loss) recognized on the TRS (see Note F – Fair Value Measurements).