Non-Controlling Interests, Preferred Shares, Common Shares and Common Shares in Treasury - Non-Controlling Interests (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Noncontrolling Interest [Line Items]
Non-controlling interests	$ 13,800,000	$ 21,600,000
Operating partnership units	7,400,000	7,400,000
Non-controlling interests, total	24,322,000	32,208,000
Shopping centers and development parcels in various states [Member]
Noncontrolling Interest [Line Items]
Non-controlling interests	$ 3,100,000	$ 3,200,000