Mortgage Revenue Bonds - Schedule of Percentage of MRBs Principal Outstanding (Details)	Dec. 31, 2020	Dec. 31, 2019
TX [Member]
Schedule Of Available For Sale Securities [Line Items]
Percentage of available for sale securities by location	43.00%	43.00%
CA [Member]
Schedule Of Available For Sale Securities [Line Items]
Percentage of available for sale securities by location	17.00%	18.00%
SC [Member]
Schedule Of Available For Sale Securities [Line Items]
Percentage of available for sale securities by location	17.00%	17.00%