Discontinued Operations and Gain (Loss) on Disposition of Rental Properties (Details 2) (USD $)	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties	$ 133,554,000	$ 51,303,000	$ 5,720,000
Waterfront Station - East 4th & West 4th Buildings [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties	111,738,000
250 Huron (Office Building) [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties	9,428,000
Charleston Marriott hotel [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties	9,957,000
Ritz Carlton [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties	2,431,000
Simi Valley Town Center (Regional Mall) [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties		46,802,000
Saddle Rock Village [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties		(1,428,000)
Grand Avenue [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties			4,548,000
Other [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties		(275,000)	1,172,000
101 San Fernando (Apartment Community) [Member]
Gain Loss on Disposition of Rental Properties
Gain (Loss) on disposition of rental properties		$ 6,204,000