Net Gain on Disposition of Partial Interests in Rental Properties (Details) (USD $)	3 Months Ended			9 Months Ended		12 Months Ended
	Oct. 31, 2013	Jul. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012	Jan. 31, 2012
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties	$ 491,160,000		$ 0	$ 496,092,000	$ 0
QIC 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	381,627,000		0	381,627,000	0
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	$ 109,533,000	$ 4,932,000	$ 0	$ 114,465,000	$ 0	$ 9,561,000