Net Gain on Disposition of Partial Interests in Rental Properties (Details Textual) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended	12 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013 New York Retail Joint Venture [Member]	Jul. 31, 2013 New York Retail Joint Venture [Member]	Jan. 31, 2012 New York Retail Joint Venture [Member]	Jan. 31, 2013 New York Retail Joint Venture [Member]	Mar. 29, 2011 New York Retail Joint Venture [Member] properties
Net Gain on Disposition of Partial Interests in Rental Properties (Textual) [Abstract]
Percentage of ownership sold									49.00%
Number of properties held by newly formed joint venture									15
Nonrecourse mortgage debt on the properties assumed by the outside partner									$ 244,952,000
Proceeds in the form of loan from the joint venture							178,286,000
Outside partner's minimum initial investment requirement									20.00%
Net gain on disposition of partial interests in rental properties	4,932,000	0	4,932,000	0	4,932,000	4,932,000	9,561,000
Deferred gains recorded in exchange of ownership interests					$ 109,533,000	$ 109,533,000		$ 114,465,000