Net Gain (Loss) on Disposition of Partial Interests in Rental Properties and Other Investment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	$ 0	$ 17,665	$ 257,990
New York Retail Joint Venture [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	0	9,561	0
Stonecrest Mall Joint Venture [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	0	5,849	0
Annex Building Adjacent to the Dallas Wilson Building [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	0	2,255	0
University Park Joint Venture [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	0	0	176,192
Nets [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	0	0	55,112
Bernstein Joint Venture [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	0	0	29,342
Other Transaction Costs [Member]
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties and other investment	$ 0	$ 0	$ (2,656)