Mortgage Debt and Notes Payable, Nonrecourse (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013	Jan. 31, 2012
Mortgage Debt and Notes Payable Nonrecourse Collateralized by Real Estate Properties [Abstract]
Fixed	$ 3,758,144	$ 3,419,685
Total weighted average rate	5.51%	5.65%
Variable
Taxable	1,510,930	1,802,629
Weighted average rate, taxable	4.93%	4.76%
Tax-Exempt	471,586	437,209
Weighted average rate, tax-exempt	1.64%	1.55%
Mortgage debt and Notes Payable, Nonrecourse	5,740,660	5,659,523
Weighted Average Rate Mortgage Debt and Notes Payable Nonrecourse	5.04%	5.05%
Operating Properties [Member]
Mortgage Debt and Notes Payable Nonrecourse Collateralized by Real Estate Properties [Abstract]
Fixed	3,456,879	3,008,293
Variable
Taxable	1,448,205	1,378,585
Tax-Exempt	408,785	421,434
Mortgage debt and Notes Payable, Nonrecourse	5,313,869	4,808,312
Development Projects [Member]
Mortgage Debt and Notes Payable Nonrecourse Collateralized by Real Estate Properties [Abstract]
Fixed	299,565	406,619
Variable
Taxable	62,725	409,733
Tax-Exempt	53,500	0
Mortgage debt and Notes Payable, Nonrecourse	415,790	816,352
Total gross commitment fom lenders	705,983	1,338,181
Land Projects [Member]
Mortgage Debt and Notes Payable Nonrecourse Collateralized by Real Estate Properties [Abstract]
Fixed	1,700	4,773
Variable
Taxable	0	14,311
Tax-Exempt	9,301	15,775
Mortgage debt and Notes Payable, Nonrecourse	11,001	34,859
Total gross commitment fom lenders	$ 11,001	$ 35,058