Net Gain on Disposition of Partial Interests in Rental Properties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Apr. 30, 2012	Apr. 30, 2011
Net gain on disposition of partial interests in rental properties and other investments
Net gain on disposition of partial interests in rental properties	$ 0	$ 9,561
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	$ 0	$ 9,561

The difference between the book value and the sale price of other nonspecific investments. This element is used when other, more specific, elements are not appropriate. This element refers to the gain (loss) included in earnings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Name:	us-gaap_GainLossOnSaleOfOtherInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration