Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended															12 Months Ended
	Dec. 31, 2012 segment properties	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Building and Building Improvements [Member] Minimum [Member]	Dec. 31, 2012 Building and Building Improvements [Member] Maximum [Member]	Dec. 31, 2012 Minor Improvements, Furniture and Equipment [Member] Minimum [Member]	Dec. 31, 2012 Minor Improvements, Furniture and Equipment [Member] Maximum [Member]	Dec. 31, 2012 Plaza El Segundo [Member]	Dec. 31, 2011 Plaza El Segundo [Member]	Dec. 30, 2011 Plaza El Segundo [Member]	Dec. 31, 2012 Melville Mall [Member]	Dec. 31, 2011 Melville Mall [Member]	Oct. 16, 2006 Melville Mall [Member] year	Oct. 16, 2021 Melville Mall [Member] Purchased Call Option [Member]	Oct. 16, 2023 Melville Mall [Member] Put Option [Member]	Dec. 31, 2012 Commercial Real Estate [Member] Minimum [Member]	Dec. 31, 2012 Commercial Real Estate [Member] Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life				35 years	50 years	2 years	20 years
Operating Lease, Term																3 years	10 years
Allowance for Doubtful Accounts Receivable	$ 15,900,000	$ 17,600,000
Straight Line Rents, Collection Of Accounts Receivable, Period	1 year
Deferred Rent Receivables, Net	56,100,000	50,500,000
Depreciation Expense Real Estate	128,700,000	114,200,000	108,300,000
Investments Classified As Cash And Cash Equivalents, Initial Maturity	3 months
Cash, Uninsured Amount	33,600,000
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	4,200,000
Hedging Instruments Outstanding			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	760,789,000	747,523,000						183,900,000	185,600,000		21,400,000	22,100,000
Real estate, net	3,555,379,000	3,298,856,000						189,400,000	194,600,000		63,100,000	64,000,000
Maximum period of sale to defer gain on sale of other property, days	180
Business Acquisition, Percentage of Voting Interests Acquired										48.20%
Real Estate Maximum Exposure to Loss								17,500,000
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