Summary of Significant Accounting Policies - Narrative (Details)		3 Months Ended
	Mar. 31, 2019 USD ($) tenant Property lease_option store shares	Mar. 31, 2019 USD ($) tenant Property lease_option store shares	Mar. 31, 2018 USD ($) shares	Jan. 01, 2019	Dec. 31, 2018 USD ($)
Significant Accounting Policies [Line Items]
Number of tenants | tenant	1	1
Number of shopping centers | store	32	32
Percentage of ownership in operating partnership		74.40%
Accounts receivable, net representing rental income accrued	$ 43,200,000	$ 43,200,000			$ 43,300,000
Period expected for the sale of property to occur		1 year
Deferred debt costs	10,354,000	$ 10,354,000			10,300,000
Accumulated amortization, deferred debt costs	7,000,000	7,000,000			7,300,000
Deferred leasing costs, net	26,967,000	26,967,000			28,083,000
Accumulated amortization deferred leasing cost	$ 38,600,000	38,600,000			37,700,000
Amortization expense deferred leasing cost		1,600,000	$ 1,400,000
Interest capitalized		$ 2,146,000	1,144,000
Commercial development projects, availability for occupancy, maximum period after major construction activity		1 year
Depreciation expense		$ 10,000,000	9,900,000
Repairs and maintenance expense		$ 3,700,000	$ 3,100,000
Shares credited to directors' deferred fee accounts (in shares) | shares	109,696	1,617
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares) | shares		485	8,088
Right-of-use asset	$ 2,100,000	$ 2,100,000
Operating lease liability	$ 2,200,000	$ 2,200,000
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	$ 30,800	$ 30,800			$ 58,500
Operating lease term of contract				1 year
Minimum | Building
Significant Accounting Policies [Line Items]
Estimated useful life (in years)		35 years
Maximum
Significant Accounting Policies [Line Items]
Operating lease term of contract				15 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
Giant Food
Significant Accounting Policies [Line Items]
Percentage of total revenue		4.60%
Number of shopping centers | store		10
Revenues
Significant Accounting Policies [Line Items]
Number of tenants | tenant	1	1
Percentage of total revenue		2.50%
Common Stock
Significant Accounting Policies [Line Items]
Shares due to exercise of employee stock options and issuance of directors' deferred stock (in shares) | shares		6,565
Corporate Headquarters
Significant Accounting Policies [Line Items]
Number of options to extend lease | lease_option	1	1
Lease renewal term				5 years