Note 13 - Related Party Transactions - (Details Textual)		3 Months Ended		9 Months Ended
	Dec. 27, 2020 Merger shares	Sep. 30, 2021 USD ($) property	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) property	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction [Line Items]
Receivables due from related parties | $		$ 300,000		$ 300,000		$ 500,000
Revenue from related parties | $		$ 300,000	$ 400,000	$ 1,100,000	$ 1,200,000
Number of properties to be acquired | property		2		2
Ground lease revenues | $		$ 7,007,000	5,232,000	$ 17,623,000	14,541,000
Cromwell Field Shopping Center [Member]
Related Party Transaction [Line Items]
Ground lease revenues | $					100,000
BBL Property [Member]
Related Party Transaction [Line Items]
Ownership interest percentage		0.00%		0.00%
Broad Street Entities [Member]
Related Party Transaction [Line Items]
Number of Mergers Remaining | Merger	2
Thomas M. Yockey [Member] | Broad Street Entities [Member] | Common Stock [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	17,985
Thomas M. Yockey [Member] | Broad Street Entities [Member] | Common Stock [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	2,533,650
Thomas M. Yockey [Member] | Broad Street Entities [Member] | OP units [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	136,213
Thomas M. Yockey [Member] | Broad Street Entities [Member] | OP units [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	420,523
Michael Z. Jacoby [Member] | Broad Street Entities [Member] | Common Stock [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	17,985
Michael Z. Jacoby [Member] | Broad Street Entities [Member] | Common Stock [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	2,533,650
Michael Z. Jacoby [Member] | Broad Street Entities [Member] | OP units [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	136,213
Michael Z. Jacoby [Member] | Broad Street Entities [Member] | OP units [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	856,805
Alexander Topchy [Member] | Broad Street Entities [Member] | Common Stock [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	1,934
Alexander Topchy [Member] | Broad Street Entities [Member] | Common Stock [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	137,345
Alexander Topchy [Member] | Broad Street Entities [Member] | OP units [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	14,338
Alexander Topchy [Member] | Broad Street Entities [Member] | OP units [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	48,320
Daniel J.W. Neal [Member] | Broad Street Entities [Member] | Common Stock [Member]
Related Party Transaction [Line Items]
Remaining equity interest issued as consideration for the mergers | shares	16,450
Daniel J.W. Neal [Member] | Broad Street Entities [Member] | Common Stock [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	878,170
Samuel M. Spiritos [Member] | Broad Street Entities [Member] | Common Stock [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Related Party Transaction [Line Items]
Equity interest issued as consideration for the mergers | shares	13,827
Maximum [Member]
Related Party Transaction [Line Items]
Percentage of management fee				4.00%
Maximum [Member] | Cromwell Field Shopping Center [Member]
Related Party Transaction [Line Items]
Ground lease revenues | $			100,000	$ 100,000
Minimum [Member]
Related Party Transaction [Line Items]
Percentage of management fee				3.00%
Timbergate Ventures, LLC [Member] | Thomas M. Yockey [Member]
Related Party Transaction [Line Items]
Related party consulting agreement term				2 years
Related party consulting fees | $				$ 200,000
Related party general and administrative expenses | $		$ 50,000	50,000	150,000	150,000
Shulman Rogers LLP [Member] | Maximum [Member] | Samuel M. Spiritos [Member]
Related Party Transaction [Line Items]
Related party legal fees | $		100,000	$ 100,000	300,000	$ 100,000
Other Assets, Net [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Receivables due from related parties | $		100,000		100,000
Other Assets, Net [Member] | Due from Properties Managed by Company [Member]
Related Party Transaction [Line Items]
Receivables due from related parties | $						200,000
Payables Due to Related Parties [Member] | Due to Properties Managed by Company [Member] | Borrowed by Company for Working Capital [Member]
Related Party Transaction [Line Items]
Payables due to related parties | $						$ 700,000
Payables Due to Related Parties [Member] | Due to Properties Managed by Company [Member] | Borrowed by Company for Working Capital [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Payables due to related parties | $		100,000		100,000
Accounts Payable and Accrued Expenses [Member] | BSR [Member] | Thomas M. Yockey [Member]
Related Party Transaction [Line Items]
Consideration to be paid in exchange for repurchasing ownership interest | $								$ 1,500,000
Consideration paid in exchange for repurchasing ownership interest | $							$ 1,000,000.0
Consideration payable in exchange for repurchasing ownership interest | $		$ 500,000		$ 500,000