Net Gain on Disposition of Partial Interests in Rental Properties (Details Textual) (USD $)	3 Months Ended		12 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Jan. 31, 2012	Mar. 29, 2011 Property
Net Gain on Disposition of Partial Interests in Rental Properties (Textual) [Abstract]
Net gain on disposition of partial interests in rental properties	$ 0	$ 9,561,000
New York Retail Joint Venture [Member]
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
Net gain on disposition of partial interests in rental properties	0	9,561,000
Number of retail properties formerly wholly owned by the company				14
Percentage ownership of the company in partially owned retail property				75.00%
Nonrecourse mortgage debt on the properties assumed by the outside partner		244,952,000
Net cash proceeds in the form of loan from the joint venture			178,286,000
Transaction costs associated with gains received by the company in exchange of ownership interests		11,776,000
Deferred gains recorded in exchange of ownership interests	114,465,000
Participation payment made to the ground lessor of two properties		$ 5,779,000
Outside partner's minimum initial investment requirement			20.00%