Summary Of Significant Accounting Policies (Narrative) (Details)		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 26, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment customer property shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Common units in operating partnership | shares				7,305,355
Cash and cash equivalents maximum benchmark (in months)				3 months
Minimum expected future benefit period on expenditures cost to be capitalized and depreciated (in years)				2 years
Minimum expected future benefit period on transaction cost to be capitalized and depreciated (in years)				1 year
Length of time criteria for expected sale of assets to be classified as properties held for disposition				12 months
Below market lease, net		$ 1,800,000		$ 1,800,000		$ 2,400,000
Below market leases, accumulated amortization		12,000,000.0		12,000,000.0		11,400,000
Impairment on assets				0	$ 0
Operating lease, right-of-use asset		$ 1,500,000		$ 1,500,000		$ 1,600,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		Other Assets		Other Assets		Other Assets
Operating lease, liability		$ 1,500,000		$ 1,500,000		$ 1,600,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]		Accounts Payable and Accrued Liabilities		Accounts Payable and Accrued Liabilities		Accounts Payable and Accrued Liabilities
Accumulated amortization		$ 200,000		$ 200,000		$ 100,000
Accounts receivable, write-off		300,000		1,500,000
Deferred rent receivable, write-off		300,000		2,700,000
Rental income		103,760,000	$ 108,064,000	310,535,000	323,671,000
Rental income, operating leases		79,400,000	84,100,000	238,300,000	250,700,000
Rental income, variable lease payments		24,400,000	$ 24,000,000.0	72,200,000	$ 73,000,000.0
Income tax expense				0
Tax benefit for uncertain tax positions				$ 0		0
Number of operating segments | segment				2
Number of reportable segments | segment				1
Net real estate investment property		1,858,867,000		$ 1,858,867,000		1,889,238,000
Properties held for sale, net						15,264,000
COVID-19 [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferral agreement, number of customers | customer				388
Deferral agreement, percentage of customers on a percentage of total rental income basis				11.00%
Deferred rent receivable		1,700,000		$ 5,500,000
Rent receivable abated		300,000		1,200,000
Reclassification [Member]
Summary Of Significant Accounting Policies [Line Items]
Net real estate investment property						(3,800,000)
Properties held for sale, net						3,800,000
Above Market Leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, net		800,000		800,000		1,200,000
Finite-lived intangible assets, accumulated amortization		(10,900,000)		(10,900,000)		(10,600,000)
Acquired In Place Leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Finite-lived intangible assets, net		3,500,000		3,500,000		5,700,000
Finite-lived intangible assets, accumulated amortization		$ 6,500,000		$ 6,500,000		$ 4,100,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life (in years)				5 years
Operating lease, expiration date				2029
Operating lease, remaining lease term				9 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life (in years)				30 years
Operating lease, expiration date				2030
Operating lease, remaining lease term				9 years 3 months 18 days
Highgate at the Mile [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of Units in Multi-Family Asset | property				395
Highgate at the Mile [Member] | JV Partner [Member]
Summary Of Significant Accounting Policies [Line Items]
Consolidated entity ownership percentage		5.00%		5.00%
Brentford at The Mile [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of Units in Multi-Family Asset | property				411
Brentford at The Mile [Member] | JV Partner [Member]
Summary Of Significant Accounting Policies [Line Items]
Consolidated entity ownership percentage		1.80%		1.80%
Subsequent Event [Member] | COVID-19 [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred payments received	$ 1,300,000
Collection rate percentage on deferral repayments	98.30%