Investments in Mortgage Revenue Bonds - Schedule of MRBs Acquisitions (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) Unit	Mar. 31, 2020 Unit
Schedule Of Available For Sale Securities [Line Items]
Units | Unit		2,886
Principal Outstanding at Date of Acquisition | $	$ 6,050,000
Gateway Village [Member] | Durham NC [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	64
Maturity Date	Apr. 01, 2032
Base Interest Rate	6.10%
Principal Outstanding at Date of Acquisition | $	$ 2,600,000
Lynnhaven Apartments [Member] | Durham NC [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	75
Maturity Date	Apr. 01, 2032
Base Interest Rate	6.10%
Principal Outstanding at Date of Acquisition | $	$ 3,450,000