Accounting Policies (Details Textuals) (USD $)	6 Months Ended	12 Months Ended
	Jul. 31, 2011	Jan. 31, 2011
Accounting Policies (Textuals)
Reclassified from investments in and advances to affiliates to cash distributions and losses in excess of investments in unconsolidated investments on the consolidated balance sheet	$ 282,955,000	$ 290,492,000
Unrealized losses on an interest rate swap associated with office building	121,459,000	102,387,000
Total rate of return swap Contract amount	640,000,000	640,000,000
Interest rate on interest rate swap agreement	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)
Expected amount to be reclassified from accumulated OCI to interest expense within the next twelve months	33,168,000
Maximum loss exposure for unconsolidated variable interest entities	97,000,000
Collateralized borrowings of variable interest entities	29,000,000
Decrease in real estate due to deconsolidation of the VIE	744,999,000
Decrease in Cash and equivalents due to deconsolidation of the VIE	4,588,000
Decrease in restricted cash and escrowed funds due to deconsolidation of the VIE	66,882,000
Decrease in other assets due to deconsolidation of the VIE	18,561,000
Decrease in nonrecourse mortgage debt due to deconsolidation of the VIE	670,000,000
Decrease in account payable and accrued expenses due to deconsolidation of the VIE	35,009,000
Increase in investments and advances to affiliates due to deconsolidation of the VIE	$ 130,021,000
Residential Group [Member] | Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	18
Properties representing Variable Interest Entities	9
Commercial Group [Member] | Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	13
Properties representing Variable Interest Entities	11
Land Development Group [Member] | Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	2
Properties representing Variable Interest Entities	2
Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	33
Properties representing Variable Interest Entities	22
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entities	59