Derivative Instruments and Hedging Activities (Details Textual) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2013 swap	Jan. 31, 2012	Jan. 31, 2011
Derivative [Line Items]
Gain loss on cash flow hedges to be reclassified within next twelve months	$ 27,283
SIFMA rate	0.08%
Aggregate notional amount of TRS designated as fair value hedging instruments	266,395
Number of forward swaps outstanding	0
Net gain (loss) from change in fair value of underlying TRS borrowings recognized in interest expense	770	(11,855)	(1,924)
Adjustment for nonperformance risk	11,772
Aggregate fair value of derivative instruments in a liability position	167,496
Posted collateral consisting of cash and notes receivable	$ 89,101
Minimum [Member] | Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative instrument term of agreements	1 year
Minimum [Member] | Caps and Floors [Member]
Derivative [Line Items]
Derivative instrument term of agreements	1 year
Minimum [Member] | Treasury Options [Member]
Derivative [Line Items]
Derivative instrument term of agreements	5 years
Minimum [Member] | Forward Swaps [Member]
Derivative [Line Items]
Derivative instrument term of agreements	5 years
Maximum [Member] | Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative instrument term of agreements	10 years
Maximum [Member] | Caps and Floors [Member]
Derivative [Line Items]
Derivative instrument term of agreements	3 years
Maximum [Member] | Treasury Options [Member]
Derivative [Line Items]
Derivative instrument term of agreements	10 years
Maximum [Member] | Forward Swaps [Member]
Derivative [Line Items]
Derivative instrument term of agreements	10 years