Derivative Instruments and Hedging Activities (Details Textual) (USD $)	3 Months Ended
	Apr. 30, 2012 Derivatives	Apr. 30, 2011	Jan. 31, 2011
Derivative Instruments and Hedging Activities (Textual) [Abstract]
Gain loss on cash flow hedges to be reclassified within next twelve months	$ 27,751,000
Gain (Loss) on forward swaps not designated as hedges included in interest expense		229,000
SIFMA rate	0.25%
Aggregate notional amount of TRS designated as fair value hedging instruments	271,660,000
Duration of forward swap rate	five to ten years
Number of forward swaps outstanding	0
Aggregate notional amount of forward swaps terminated			62,800,000
Net gain (loss) recognized on change in underlying TRS borrowings recognized in interest expense	145,000	(1,482,000)
Adjustment for nonperformance risk	14,517,000
Aggregate fair value of derivative instruments in a liability position	180,017,000
Ineffectiveness of cash flow hedge included in interest expenses	0	0
Posted collateral consisting of cash and notes receivable	81,779,000
Caps and Floors [Member]
Derivative [Line Items]
Derivative Instrument Duration of agreement	one to three years
Treasury options [Member]
Derivative [Line Items]
Derivative Instrument Duration of agreement	five to ten years
Treasury options outstanding	$ 0
Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative Instrument Duration of agreement	one to ten years