Fair Value of Financial Instruments (Fair value measurements, recurring basis) (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	$ 541,070,073	$ 550,148,284
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	541,070,000	550,148,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Fair Value, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Fair Value, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	541,070,073	550,148,284
Fair Value, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0
Student Loan Pools | Fair Value, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Student Loan Pools | Fair Value, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	55,833,826	59,156,982
Student Loan Pools | Fair Value, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
SBA Bonds | Fair Value, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
SBA Bonds | Fair Value, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	91,696,061	99,629,967
SBA Bonds | Fair Value, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Tax Exempt Municipal Bonds | Fair Value, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Tax Exempt Municipal Bonds | Fair Value, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	20,919,512	21,310,328
Tax Exempt Municipal Bonds | Fair Value, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Taxable Municipal Bonds | Fair Value, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
Taxable Municipal Bonds | Fair Value, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	52,935,070	50,769,739
Taxable Municipal Bonds | Fair Value, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
MBS | Fair Value, Recurring [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	0	0
MBS | Fair Value, Recurring [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	319,685,604	319,281,268
MBS | Fair Value, Recurring [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available For Sale ("AFS")	$ 0	$ 0