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Income Tax and Distributions (Narrative) (Details) - USD ($)			12 Months Ended
	Oct. 07, 2021	Jun. 29, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Jun. 30, 2021
Income Tax And Distributions [Line Items]
REIT taxable income (loss)			$ 4,154,000	$ (11,950,000)	$ 988,000
Uncertain tax positions			0	0
Increases or decreases in uncertain tax positions due to changes in tax positions			0
Interest or penalties recognized			$ 0	0	$ 0
Tax examination year			2018 2019 2020 2021
Amount per share of distributions					$ 0.3018	$ 0.135600	$ 0.135600
Dividends payable, date declared		Jun. 29, 2021
Dividends payable, date of record	Sep. 30, 2021	Jun. 30, 2021
Dividends payable, date to be paid	Oct. 07, 2021	Jul. 26, 2021
Annualized rate on Estimated Per Share NAV					6.00%
Mainstreet Texas Development Fund, LLC ("Mainstreet JV") [Member]
Income Tax And Distributions [Line Items]
Provision for asset impairment				$ 15,405,000
Effective income tax rate				28.51%
Federal tax rate				21.00%
Deferred tax benefit related to impairment				$ 4,400,000
Full valuation allowance				4,400,000
Reduction in the valuation allowance					$ 1,560,000
Reduction in the deferred tax asset					1,560,000
Deferred tax asset					2,840,000
Income tax expense (benefit)			$ 0	$ 0	$ 0
Capital loss carryforwards			$ 9,931,000
Capital loss carryforwards expiration date			2024
Mainstreet Texas Development Fund, LLC ("Mainstreet JV") [Member] \| ILLINOIS [Member]
Income Tax And Distributions [Line Items]
State rate				9.50%
IL tax rate				7.51%
Minimum [Member]
Income Tax And Distributions [Line Items]
Percentage of adjusted REIT taxable income require to distribute among shareholders			90.00%