Note 3 - Real Estate - Summary of Geographic Concentration of Properties (Details) $ in Thousands	3 Months Ended
Mar. 31, 2021 USD ($) property	Mar. 31, 2020 USD ($)
Concentration Risk [Line Items]
Number of Properties \| property	11
Gross Real Estate Assets	$ 186,300
Geographic Concentration Risk [Member]
Concentration Risk [Line Items]
Number of Properties \| property	11
Gross Real Estate Assets	$ 186,345
Percentage of Total Real Estate Assets	100.00%
Geographic Concentration Risk [Member] \| Rental Income [Member]
Concentration Risk [Line Items]
Revenues	$ 3,938	$ 4,146
Geographic Concentration Risk [Member] \| Maryland [Member]
Concentration Risk [Line Items]
Number of Properties \| property	4
Gross Real Estate Assets	$ 76,971
Percentage of Total Real Estate Assets	41.20%
Geographic Concentration Risk [Member] \| Maryland [Member] \| Rental Income [Member]
Concentration Risk [Line Items]
Revenues	$ 1,896	2,154
Geographic Concentration Risk [Member] \| Virginia [Member]
Concentration Risk [Line Items]
Number of Properties \| property	4
Gross Real Estate Assets	$ 68,121
Percentage of Total Real Estate Assets	36.60%
Geographic Concentration Risk [Member] \| Virginia [Member] \| Rental Income [Member]
Concentration Risk [Line Items]
Revenues	$ 1,227	1,228
Geographic Concentration Risk [Member] \| Pennsylvania [Member]
Concentration Risk [Line Items]
Number of Properties \| property	1
Gross Real Estate Assets	$ 26,761
Percentage of Total Real Estate Assets	14.40%
Geographic Concentration Risk [Member] \| Pennsylvania [Member] \| Rental Income [Member]
Concentration Risk [Line Items]
Revenues	$ 511	594
Geographic Concentration Risk [Member] \| Washington, D.C. [Member]
Concentration Risk [Line Items]
Number of Properties \| property	1
Gross Real Estate Assets	$ 8,393
Percentage of Total Real Estate Assets	4.50%
Geographic Concentration Risk [Member] \| Washington, D.C. [Member] \| Rental Income [Member]
Concentration Risk [Line Items]
Revenues	$ 173	$ 170
Geographic Concentration Risk [Member] \| Colorado [Member]
Concentration Risk [Line Items]
Number of Properties \| property	1
Gross Real Estate Assets	$ 6,099
Percentage of Total Real Estate Assets	3.30%
Geographic Concentration Risk [Member] \| Colorado [Member] \| Rental Income [Member]
Concentration Risk [Line Items]
Revenues	$ 131

Percentage of real estate property investment.

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The number of real estate properties owned as of the balance sheet date.

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Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

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