Summary of Significant Accounting Policies - Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014 tenant store	Sep. 30, 2013	Sep. 30, 2014 tenant store	Sep. 30, 2013	Dec. 31, 2013
Significant Accounting Policies [Line Items]
Number of tenants	1		1
Number of shopping centers	31		31
Allowance for doubtful accounts receivables	$ 500,000		$ 500,000		$ 600,000
Period expected for the sale of property to occur			1 year
Deferred debt costs, net	10,192,000		10,192,000		9,675,000
Accumulated amortization deferred leasing cost	5,500,000		5,500,000		4,500,000
Deferred leasing costs, net	26,751,000		26,751,000		26,052,000
Accumulated amortization deferred leasing cost	20,300,000		20,300,000		16,600,000
Amortization expense deferred leasing cost			3,900,000	5,000,000
Severance payments			1,100,000
Defined benefit plan, benefits paid			814,300
Interest expensed capitalized	186,000	59,000	430,000	93,000
Commercial development projects, availability for occupancy, maximum period after major construction activity			1 year
Depreciation and amortization expense			26,800,000	34,300,000
Decrease in depreciation expense			(7,500,000)
Repairs and maintenance expense			9,200,000	7,500,000
Property operating expenses	6,316,000	6,106,000	20,039,000	18,096,000
Shares credited to directors' deferred fee accounts			229,867
Percentage of ownership in Operating Partnership			74.40%
Snow Removal Costs
Significant Accounting Policies [Line Items]
Property operating expenses			1,700,000
Van Ness Square
Significant Accounting Policies [Line Items]
Additional depreciation expense as a result of reduction in estimated useful life				8,000,000
Estimated remaining useful life				4 months
Held-for-sale
Significant Accounting Policies [Line Items]
Number of real estate properties	0		0
Minimum
Significant Accounting Policies [Line Items]
Accounts receivable, net representing rental income accrued	38,100,000		38,100,000		37,200,000
Allowance for doubtful accounts receivables representing rental income accrued	$ 300,000		$ 300,000		$ 500,000
Minimum | Building
Significant Accounting Policies [Line Items]
Estimated useful life			35 years
Maximum | Building
Significant Accounting Policies [Line Items]
Estimated useful life			50 years
Maximum | Building Improvements
Significant Accounting Policies [Line Items]
Estimated useful life			20 years
Giant Food
Significant Accounting Policies [Line Items]
Percentage of total revenue			4.50%
Number of shopping centers			9
Safeway
Significant Accounting Policies [Line Items]
Percentage of total revenue			2.50%
Number of shopping centers			8
Revenues
Significant Accounting Policies [Line Items]
Number of tenants	2		2
Percentage of total revenue			2.50%