Investment and Mortgage-Backed Securities, Available for Sale (Narrative) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) security	Sep. 30, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale		$ 572,137,595	$ 617,131,400
Available-for-sale Securities, Fair Value Disclosure		589,324,401	627,833,669
Available For Sale Securities Pledged as Collateral, Amortized Cost Basis		$ 263,300,000	$ 299,500,000
Percent of unrealized losses for securities in a continuous loss position for 12 months or more		37.00%	22.70%
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		88	71
GNMA Mortgage-Backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale		$ 91,700,000	$ 133,800,000
Available-for-sale Securities, Fair Value Disclosure		93,400,000	133,900,000
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale		37,000,000	31,400,000
Available-for-sale Securities, Fair Value Disclosure		37,700,000	$ 31,600,000
Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Gross Realized Gains	$ 1,300,000	$ 220,239