Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	$ 830,256,024		$ 742,897,488
Bond Purchase Commitments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	3,165,172		2,399,449
Taxable Bonds (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	3,931,471		4,084,599
Public housing capital fund trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	55,791,371		57,158,068
Derivative Contracts (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	521,789		383,604
Derivative Swap Liability [Member]
Schedule of Available-for-sale Securities [Line Items]
Liabilities at fair value	(1,283,437)		(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	830,256,024	$ 820,480,265	742,897,488	$ 730,475,386	$ 666,958,282	$ 653,875,949
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	3,165,172	2,620,393	2,399,449	17,218,819	7,222,173	5,634,360
Fair Value, Inputs, Level 3 [Member] | Taxable Bonds (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	3,931,471	4,179,205	4,084,599	5,294,229	4,938,104	4,824,060
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	55,791,371	$ 55,851,799	57,158,068	$ 62,180,059	$ 60,505,340	$ 60,707,290
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	521,789		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	(1,283,437)		(1,339,283)
Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	26,947,851		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	26,947,851		90,016,872
Mortgage Revenue Bonds Held In Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	741,181,807		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	$ 741,181,807		$ 590,194,179