Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 properties segment year	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Minimum [Member]	Dec. 31, 2011 Building and Building Improvements [Member] year	Dec. 31, 2011 Minor Improvements, Furniture and Equipment [Member] year	Dec. 31, 2011 Melville Mall [Member]	Dec. 31, 2010 Melville Mall [Member]	Oct. 16, 2006 Melville Mall [Member] year	Jan. 19, 2011 Tower Shops January 19 2011 [Member]	Dec. 31, 2011 Plaza El Segundo [Member]	Dec. 30, 2011 Plaza El Segundo [Member]	Oct. 16, 2021 Melville Mall [Member] Purchased Call Option [Member]	Oct. 16, 2023 Melville Mall [Member] Put Option [Member]	Dec. 30, 2011 Plaza El Segundo [Member]
Summary of Significant Accounting Policies [Line Items]
Balance Sheet Impact of Reclassification	$ 65,000,000
Reclassification Impact to Shareholders Equity	65,000,000
Reclassification Impact to Redeemable Noncontrolling Interests	65,000,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Below Market Lease Liabilities										4,400,000
Temporary Equity, Accretion to Redemption Value	300,000
Allowance for Doubtful Accounts Receivable	17,600,000	18,700,000
Straight Line Rents, Collection Of Accounts Receivable, Period				1 year
Accounts Receivable Straight-line Rents	50,500,000	45,600,000
Property, Plant and Equipment, Useful Life, Minimum					35	3
Property, Plant and Equipment, Useful Life, Maximum					50	20
Depreciation Expense Real Estate	114,200,000	108,300,000	103,700,000
Investments Classified As Cash And Cash Equivalents, Initial Maturity	3 months
Cash, Uninsured Amount	64,300,000
Split Dollar Insurance Premiums Paid	4,600,000	4,600,000
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	3,600,000
Hedging Instruments Outstanding		0	0
Residual Profit Maxiumum	50.00%
Master Lease Term									20
Secured Debt F R T									34,200,000
Purchase Price Under Option													5,000,000	5,000,000
Mortgages payable	747,523,000	529,501,000					22,100,000	22,800,000
Real estate, net	3,306,956,000	2,860,738,000					64,000,000	64,800,000
Maximum period of sale to defer gain on sale of other property, days										180
Business Acquisition, Percentage of Voting Interests Acquired												48.20%
Business Acquisition Purchase Price												192,700,000
Mortgage loan face amount										41,000,000		175,000,000			175,000,000
Mortgage loan fair value										42,900,000					185,600,000
Real Estate Maximum Exposure to Loss											8,500,000
Minimum Percentage Of Taxable Income Distributed To Shareholders	90.00%
Unrecognized Tax Benefits	$ 0	$ 0
Number of Properties Exceeding Segment Reporting Threshold	0
Segment Reporting, Factors Used to Identify Entity's Reportable Segments	10% of our revenues or property operating income
Number of Segments	1
Commercial Property Lease Term Minimum	3
Commercial Property Lease Term Maximum	10