Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	$ 810,176,708	$ 843,675,611
Bond Purchase Commitments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	2,027,473	3,002,540
Public housing capital fund trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	48,939,254	49,641,588
Taxable Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	2,397,825	2,422,459
Derivative Contracts (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	1,194,442	597,221
Derivative Swap Liability [Member]
Schedule of Available-for-sale Securities [Line Items]
Liabilities at fair value	(341,740)	(826,852)
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	810,176,708	843,675,611	$ 820,480,265	$ 742,897,488
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	2,027,473	3,002,540	2,620,393	2,399,449
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	48,939,254	49,641,588	55,851,799	57,158,068
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	2,397,825	2,422,459	$ 4,179,205	$ 4,084,599
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	1,194,442	597,221
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	(341,740)	(826,852)
Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	74,758,296	77,971,208
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	74,758,296	77,971,208
Mortgage Revenue Bonds Held In Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	681,201,158	710,867,447
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	$ 681,201,158	$ 710,867,447