Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - USD ($)	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	$ 780,166,845		$ 796,696,304
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	780,166,845	$ 773,607,185	796,696,304	$ 789,111,076	$ 762,536,041	$ 818,340,970
Bond Purchase Commitment [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	392,515		431,879
Bond Purchase Commitment [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	392,515	310,909	431,879
Taxable Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	1,462,862		1,510,437
Taxable 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	1,462,862	$ 1,443,988	1,510,437	$ 1,456,279	$ 1,417,654	$ 1,383,237
Derivative Financial Instruments (Reported within Other Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	321,372		321,503
Derivative Financial Instruments (Reported within Other Assets) [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	321,372		321,503
Mortgage Revenue Bonds Held In Trust [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	760,538,644		768,468,644
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	760,538,644		768,468,644
Mortgage Revenue Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Assets at Fair Value	17,451,452		25,963,841
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	$ 17,451,452		$ 25,963,841