Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) tenant Property store	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) tenant Property store shares	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Significant Accounting Policies [Line Items]
Number of tenants | tenant	1		1
Number of shopping centers | store	32		32
Percentage of ownership in operating partnership			74.30%
Allowance for doubtful accounts receivables	$ 300		$ 300		$ 2,000
Accounts receivable, net representing rental income accrued	44,000		$ 44,000		43,100
Period expected for the sale of property to occur			1 year
Deferred debt costs	6,759		$ 6,759		7,500
Accumulated amortization, deferred debt costs	8,300		8,300		7,300
Deferred leasing costs, net	27,679		27,679		25,983
Accumulated amortization deferred leasing cost	34,000		34,000		30,400
Amortization expense deferred leasing cost			4,100	$ 4,400
Interest capitalized	$ 900	$ 506	$ 2,495	1,762
Commercial development projects, availability for occupancy, maximum period after major construction activity			1 year
Depreciation expense			$ 30,300	29,000
Repairs and maintenance expense			$ 8,500	$ 9,200
Shares credited to directors' deferred fee accounts (in shares) | shares			181,899
Held-for-sale
Significant Accounting Policies [Line Items]
Number of real estate properties | Property	0		0
Minimum
Significant Accounting Policies [Line Items]
Allowance for doubtful accounts receivables representing rental income accrued	$ 100		$ 100		$ 500
Minimum | Building
Significant Accounting Policies [Line Items]
Estimated useful life (in years)			35 years
Maximum | Building
Significant Accounting Policies [Line Items]
Estimated useful life (in years)			50 years
Maximum | Building Improvements
Significant Accounting Policies [Line Items]
Estimated useful life (in years)			20 years
Albertson's/Safeway
Significant Accounting Policies [Line Items]
Lease termination fee			$ 3,600
Giant Food
Significant Accounting Policies [Line Items]
Percentage of total revenue			4.60%
Number of shopping centers | store			10
Capital One
Significant Accounting Policies [Line Items]
Percentage of total revenue			2.80%
Number of shopping centers | store			18
Revenues
Significant Accounting Policies [Line Items]
Number of tenants | tenant	2		2
Percentage of total revenue			2.50%
Glebe Road Construction Loan
Significant Accounting Policies [Line Items]
Deferred debt costs	$ 1,700		$ 1,700