Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2012	Jan. 31, 2012
Fair Value of nonrecourse mortgage debt and notes payable (including land held for divestiture debt), bank revolving credit facility and senior and subordinated debt
Carrying value	$ 6,728,486	$ 6,698,052
Fair Value	7,110,457	7,061,498
Fixed Rate Debt [Member]
Fair Value of nonrecourse mortgage debt and notes payable (including land held for divestiture debt), bank revolving credit facility and senior and subordinated debt
Carrying value	4,622,503	4,458,214
Fair Value	4,917,174	4,719,636
Variable Rate Debt [Member]
Fair Value of nonrecourse mortgage debt and notes payable (including land held for divestiture debt), bank revolving credit facility and senior and subordinated debt
Carrying value	2,105,983	2,239,838
Fair Value	$ 2,193,283	$ 2,341,862