Net Gain on Disposition of Partial Interests in Rental Properties and Other Investment (Details) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2011	Jul. 31, 2010
Net gain (Loss) on disposition of partial interests in rental properties and other investment
Gain loss on sale of other investments	$ 0	$ 259,381	$ 9,561	$ 260,247
New York Retail Joint Venture [Member]
Net gain (Loss) on disposition of partial interests in rental properties and other investment
Gain loss on sale of other investments	0	0	9,561	0
University Park Joint Venture [Member]
Net gain (Loss) on disposition of partial interests in rental properties and other investment
Gain loss on sale of other investments	0	204,269	0	175,793
The Nets [Member]
Net gain (Loss) on disposition of partial interests in rental properties and other investment
Gain loss on sale of other investments	0	55,112	0	55,112
Bernstein Joint Venture [Member]
Net gain (Loss) on disposition of partial interests in rental properties and other investment
Gain loss on sale of other investments	$ 0	$ 0	$ 0	$ 29,342