Derivative Instruments and Hedging Activities (Details Textual) (USD $)	3 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Derivative [Line Items]
Gain loss on cash flow hedges to be reclassified within next twelve months	$ 26,434,000
SIFMA rate	0.22%
Aggregate notional amount of TRS designated as fair value hedging instruments	257,365,000
Net gain (loss) from change in fair value of underlying TRS borrowings recognized in interest expense	94,000	145,000
Adjustment for nonperformance risk	11,557,000
Aggregate fair value of derivative instruments in a liability position	167,250,000
Posted collateral consisting of cash and notes receivable	87,849,000
Forward Starting Swaps and Treasury Options [Member]
Derivative [Line Items]
Forward starting swaps or Treasury options outstanding	$ 0
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
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