Summary of Significant Accounting Policies - Statement of Cash Flows and Supplemental Disclosure of Non-Cash Investing and Financing Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Mortgages and liability assumed from acquisitions	$ 42,300,000	$ 137,800,000	$ 0
Consolidation of the net assets (excluding mortgages disclosed below) of previously unconsolidated joint ventures	383,000,000	87,800,000	0
Mortgages assumed of previously unconsolidated joint ventures	246,200,000	50,100,000	0
Deconsolidation of net assets from the adoption of ASC 810	0	0	20,200,000
Reduction of non-controlling interests from the adoption of ASC 810	0	0	12,400,000
Deconsolidation of net assets	0	5,000,000	15,200,000
Reduction of non-controlling interests due to deconsolidation of Mervyns Joint Venture	0	0	3,900,000
Foreclosure of note receivable and transfer of collateral	0	0	19,000,000
Equity derivative liability - affiliate	0	74,300,000	0
Write-off of Preferred Share original issuance costs	5,804,000	6,402,000	0
Dividends declared	44,210,000	29,128,000	12,100,000
Accounts payable related to construction in progress	$ 18,200,000	$ 3,400,000	$ 3,300,000