Investment and Mortgage-Backed Securities, Available for Sale (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	$ 466,246,618		$ 408,695,280
Available-for-sale Securities, Fair Value Disclosure	469,324,205		414,644,840
Available For Sale Securities Pledged as Collateral, Amortized Cost Basis	204,500,000		$ 171,400,000
Proceeds From Sale of Available For Sale Securities Including Mortgage Backed Securities	$ 11,100,000	$ 6,600,000
Percent of unrealized losses for securities in a continuous loss position for 12 months or more	33.70%		39.60%
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	72		69
Available-for-sale Securities, Gross Realized Losses	$ 0	8,000
GNMA Mortgage-Backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale	69,900,000		$ 63,200,000
Available-for-sale Securities, Fair Value Disclosure	70,200,000		63,900,000
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	28,000,000		15,800,000
Available-for-sale Securities, Fair Value Disclosure	27,100,000
Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Gross Realized Gains	$ 707,000	$ 299,000	$ 0