Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	$ 843,675,611	$ 742,897,488
Bond Purchase Commitments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	3,002,540	2,399,449
Public housing capital fund trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	49,641,588	57,158,068
Taxable Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	2,422,459	4,084,599
Derivative Contracts (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	597,221	383,604
Derivative Swap Liability [Member]
Schedule of Available-for-sale Securities [Line Items]
Liabilities at fair value	(826,852)	(1,339,283)
Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	843,675,611	742,897,488	$ 653,875,949	$ 520,951,907
Fair Value, Inputs, Level 3 [Member] | Bond Purchase Commitments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	3,002,540	2,399,449	5,634,360	5,780,413
Fair Value, Inputs, Level 3 [Member] | Public housing capital fund trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	49,641,588	57,158,068	60,707,290	61,263,123
Fair Value, Inputs, Level 3 [Member] | Taxable Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	2,422,459	4,084,599	$ 4,824,060	$ 4,616,565
Fair Value, Inputs, Level 3 [Member] | Derivative Contracts (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	597,221	383,604
Fair Value, Inputs, Level 3 [Member] | Derivative Swap Liability [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liabilities Value	(826,852)	(1,339,283)
Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	77,971,208	90,016,872
Mortgage Revenue Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	77,971,208	90,016,872
Mortgage Revenue Bonds Held In Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	710,867,447	590,194,179
Mortgage Revenue Bonds Held In Trust [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 710,867,447	$ 590,194,179