Investments in Mortgage Revenue Bonds ("MRBs") - Schedule of MRB Acquisitions (Details)	3 Months Ended
	Mar. 31, 2017 USD ($) Unit
Schedule Of Available For Sale Securities [Line Items]
Principal Outstanding at Date of Acquisition	$ 59,585,000
Avistar at Copperfield [Member] | Series A [Member] | Houston, Texas [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	192
Maturity Date	May 01, 2054
Base Interest Rate	5.75%
Principal Outstanding at Date of Acquisition	$ 10,000,000
Avistar at Copperfield [Member] | Series B [Member] | Houston, Texas [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	192
Maturity Date	Jun. 01, 2054
Base Interest Rate	12.00%
Principal Outstanding at Date of Acquisition	$ 4,000,000
Avistar at Wilcrest [Member] | Series A [Member] | Houston, Texas [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	88
Maturity Date	May 01, 2054
Base Interest Rate	5.75%
Principal Outstanding at Date of Acquisition	$ 3,775,000
Avistar at Wilcrest [Member] | Series B [Member] | Houston, Texas [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	88
Maturity Date	Jun. 01, 2054
Base Interest Rate	12.00%
Principal Outstanding at Date of Acquisition	$ 1,550,000
Avistar at Wood Hollow [Member] | Series A [Member] | Austin, Texas [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	409
Maturity Date	May 01, 2054
Base Interest Rate	5.75%
Principal Outstanding at Date of Acquisition	$ 31,850,000
Avistar at Wood Hollow [Member] | Series B [Member] | Austin, Texas [Member]
Schedule Of Available For Sale Securities [Line Items]
Month Acquired	February
Units | Unit	409
Maturity Date	Jun. 01, 2054
Base Interest Rate	12.00%
Principal Outstanding at Date of Acquisition	$ 8,410,000