Subsequent Events (Details) - USD ($)				12 Months Ended
	Feb. 21, 2018	Jan. 24, 2018	Jan. 18, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 20, 2018	Jan. 29, 2018
Subsequent Event [Line Items]
Purchase Price				$ 254,532,000	$ 756,842,000
Proceeds from the disposition of properties				260,711,000	150,378,000	$ 168,895,000
Proceeds from notes receivable				32,000,000	42,819,000	$ 15,984,000
Stock repurchase authorized amount				20,000,000.0
Fund V
Subsequent Event [Line Items]
Purchase Price				167,240,000
Fund IV
Subsequent Event [Line Items]
Purchase Price				44,492,000	237,250,000
Mortgages
Subsequent Event [Line Items]
Borrowings, amount				162,900,000.0
Core Portfolio
Subsequent Event [Line Items]
Purchase Price				42,800,000	$ 519,592,000
Core Portfolio | $150 Million Term Loan | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity				$ 150,000,000.0
Subsequent Event
Subsequent Event [Line Items]
Maximum borrowing capacity							$ 300,000,000.0
Stock repurchase authorized amount							200,000,000.0
Subsequent Event | Other Secured Financings
Subsequent Event [Line Items]
Maximum borrowing capacity							40,400,000.0
Subsequent Event | 108 W. Broughton And 110 W. Broughton Street Properties | Fund IV | Disposed of by sale
Subsequent Event [Line Items]
Proceeds from the disposition of properties			$ 8,000,000
Subsequent Event | Plaza Santa Fe | Mortgages | Fund V
Subsequent Event [Line Items]
Borrowings, amount		$ 22,900,000.0
Subsequent Event | New Towne Plaza | Mortgages | Fund V
Subsequent Event [Line Items]
Borrowings, amount								$ 16,900,000.0
Subsequent Event | Senior Unsecured Credit Facility | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity							500,000,000.0
Subsequent Event | Revolving Credit Facility | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity							150,000,000.0
Subsequent Event | $300 Million Term Loan | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity							350,000,000.0
Subsequent Event | $150 Million Term Loan | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity							150,000,000.0
Subsequent Event | Trussville, Alabama | Shopping Center | Fund V
Subsequent Event [Line Items]
Purchase Price	$ 45,200,000
Subsequent Event | Core Portfolio
Subsequent Event [Line Items]
Proceeds from notes receivable		$ 26,000,000
Subsequent Event | Core Portfolio | Revolving Credit Facility | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity							150,000,000.0
Subsequent Event | Core Portfolio | $150 Million Term Loan | Unsecured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity							$ 150,000,000.0