Fair Value of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	$ 795,630,926		$ 843,675,611
Bond Purchase Commitments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	1,046,445		3,002,540
Public housing capital fund trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	48,741,478		49,641,588
Taxable Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	2,339,902		2,422,459
Derivative Instruments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	1,063,975		597,221
Derivative Swap Liability [Member]
Schedule of Available-for-sale Securities [Line Items]
Liabilities at fair value	(26,798)		(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	795,630,926	$ 820,950,642	843,675,611	$ 840,743,086	$ 830,256,024	$ 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	1,046,445	994,685	3,002,540	3,355,047	3,165,172	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	48,741,478	49,070,710	49,641,588	54,913,748	55,791,371	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	2,339,902	$ 2,357,952	2,422,459	$ 3,929,761	$ 3,931,471	$ 4,084,599
Fair Value, Inputs, Level 3 [Member] | Derivative Instruments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	1,063,975		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	(26,798)		(826,852)
Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	63,765,212		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	63,765,212		77,971,208
Mortgage Revenue Bonds Held In Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	678,700,712		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	$ 678,700,712		$ 710,867,447