Derivative Instruments and Hedging Activities (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Derivative [Line Items]
Gain loss on cash flow hedges to be reclassified within next twelve months			$ 25,643,000
SIFMA rate	0.05%		0.05%
Aggregate notional amount of TRS destinated as fair value hedging instruments	640,000,000		640,000,000
Net gain (loss) from change in fair value of underlying TRS borrowings recognized in interest expense	(1,320,000)	225,000	(1,226,000)	370,000
Adjustment for nonperformance risk	9,818,000		9,818,000
Aggregate fair value of derivative instruments in a liability position	145,993,000		145,993,000
Posted collateral consisting of cash and notes receivable	115,730,000		115,730,000
Forward Starting Swaps and Treasury Options [Member]
Derivative [Line Items]
Aggregate notional amount of TRS destinated as fair value hedging instruments	0		0
Minimum [Member] | Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative, Term of Contract			1 year
Minimum [Member] | Caps and Floors [Member]
Derivative [Line Items]
Derivative, Term of Contract			1 year
Minimum [Member] | Treasury Options [Member]
Derivative [Line Items]
Derivative, Term of Contract			5 years
Maximum [Member] | Interest rate swap agreements [Member]
Derivative [Line Items]
Derivative, Term of Contract			10 years
Maximum [Member] | Caps and Floors [Member]
Derivative [Line Items]
Derivative, Term of Contract			3 years
Maximum [Member] | Treasury Options [Member]
Derivative [Line Items]
Derivative, Term of Contract			10 years
Designated as Hedging Instrument [Member] | Total Return Swap [Member]
Derivative [Line Items]
Aggregate notional amount of TRS destinated as fair value hedging instruments	285,845,000		285,845,000
Cash Flow Hedging [Member]
Derivative [Line Items]
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness early termination of interest rate swap	$ 597,000		$ 597,000