Accounting Policies (Details Textual) (USD $)	3 Months Ended	12 Months Ended
	Apr. 30, 2012	Jan. 31, 2012
Accounting Policies (Textual) [Abstract]
Unrealized losses on an interest rate swap associated with office building	$ 136,517,000	$ 143,303,000
Total rate of return swap contract amount	640,000,000	640,000,000
All in Lender Interest Rate on Mortgage	interest rate of 6.40% (5.50% swap rate plus 0.90% lender spread)	interest rate of 6.40% (5.50% swap rate plus 0.90% lender spread)
Maximum loss exposure for unconsolidated variable interest entities	67,000,000
Collateralized borrowings of variable interest entities	$ 29,000,000
Nonrecourse Mortgage Debt [Member]
Debt Instrument [Line Items]
Swap Rate	5.50%	5.50%
All in Lender Interest Rate	6.40%	6.40%
Debt instrument variable rate basis spread	0.90%	0.90%
Maturity date of Swap Agreement	Sep. 01, 2017	Sep. 01, 2017
Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	32
Properties representing Variable Interest Entities	21
Primary Beneficiary [Member] | Commercial Group [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	14
Properties representing Variable Interest Entities	12
Primary Beneficiary [Member] | Residential Group [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	16
Properties representing Variable Interest Entities	7
Primary Beneficiary [Member] | Land Development Group [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	2
Properties representing Variable Interest Entities	2
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	60