Subsequent Events (Details)	1 Months Ended	9 Months Ended
	Oct. 31, 2015 USD ($) credit_line extension_option	Sep. 30, 2015 USD ($) credit_line
Unsecured lines of credit
Subsequent Event [Line Items]
Number of debt instruments | credit_line		3
Total Capacity, line of credit		$ 1,300,000,000
Annual facility Fee (percent)		0.30%
Mortgage and other indebtedness amount carrying value		$ 832,098,000
Unsecured lines of credit | Subsequent Event
Subsequent Event [Line Items]
Number of debt instruments | credit_line	3
Total Capacity, line of credit	$ 1,100,000,000
Unsecured lines of credit | LIBOR
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)		1.40%
Unsecured lines of credit | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Debt Instrument, increase (decrease) in variable interest rate	(0.25%)
Unsecured lines of credit 3 and 4 | Subsequent Event
Subsequent Event [Line Items]
Number of debt instruments | credit_line	2
Total Capacity, line of credit	$ 500,000,000
Unsecured line of credit 5 | Subsequent Event
Subsequent Event [Line Items]
Total Capacity, line of credit	$ 100,000,000
Debt instrument, option extension term (in years)	1 year
Unsecured line of credit 3 | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, option extension term (in years)	1 year
Unsecured line of credit 4 | Subsequent Event
Subsequent Event [Line Items]
Total Capacity, line of credit	$ 500,000,000
Unsecured term loan 4 | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, option extension term (in years)	1 year
Mortgage and other indebtedness amount carrying value	$ 350,000,000
Number of extension options available | extension_option	2
Minimum | Unsecured lines of credit
Subsequent Event [Line Items]
Annual facility Fee (percent)		0.15%
Minimum | Unsecured lines of credit | Subsequent Event
Subsequent Event [Line Items]
Annual facility Fee (percent)	0.125%
Minimum | Unsecured lines of credit | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	0.875%
Minimum | Unsecured term loan 4 | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	0.90%
Maximum | Unsecured lines of credit | Subsequent Event
Subsequent Event [Line Items]
Annual facility Fee (percent)	0.30%
Maximum | Unsecured lines of credit | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	1.55%
Maximum | Unsecured term loan 4 | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	1.75%
Weighted Average | Unsecured lines of credit | Subsequent Event
Subsequent Event [Line Items]
Annual facility Fee (percent)	0.25%
Weighted Average | Unsecured lines of credit | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	1.20%
Weighted Average | Unsecured term loan 4 | LIBOR | Subsequent Event
Subsequent Event [Line Items]
Loan agreement, basis spread on variable rate (as a percentage)	1.35%
Oak Park Mall
Subsequent Event [Line Items]
Stated Interest Rate (as a percentage)		5.85%
Oak Park Mall | Subsequent Event
Subsequent Event [Line Items]
Company's Ownership Interest (as a percent)	50.00%
Stated Interest Rate (as a percentage)	3.97%
Eastgate Crossing | Subsequent Event
Subsequent Event [Line Items]
Earn Out Proceeds, Amount Earned	$ 625,000
Earn out proceeds	1,740,000
Net proceeds from related to the lease of a tenant space	574,000
Non-recourse loans on operating properties | Oak Park Mall
Subsequent Event [Line Items]
Mortgage and other indebtedness amount carrying value		$ 275,700,000
Non-recourse loans on operating properties | Oak Park Mall | Subsequent Event
Subsequent Event [Line Items]
Mortgage and other indebtedness amount carrying value	$ 276,000,000