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Investment and Mortgage-Backed Securities, Available for Sale (Narrative) (Details)
3 Months Ended 6 Months Ended
Mar. 31, 2020
USD ($)
Jun. 30, 2020
USD ($)
security
Jun. 30, 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   $ 456,753,017   $ 408,695,280
Available-for-sale Securities, Fair Value Disclosure   471,931,623   414,644,840
Available For Sale Securities Pledged as Collateral, Amortized Cost Basis   221,600,000   $ 171,400,000
Proceeds From Sale of Available For Sale Securities Including Mortgage Backed Securities   $ 20,400,000 $ 61,900,000  
Percent of unrealized losses for securities in a continuous loss position for 12 months or more   64.70%   39.60%
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security   93   69
Available-for-sale Securities, Gross Realized Losses   $ 0 283,000  
GNMA Mortgage-Backed Securities        
Debt Securities, Available-for-sale [Line Items]        
Amortized Cost of Investment And Mortgage-Backed Securities Available For Sale   68,000,000.0   $ 63,200,000
Available-for-sale Securities, Fair Value Disclosure   69,800,000   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   32,000,000.0   $ 15,800,000
Available-for-sale Securities, Fair Value Disclosure   32,600,000    
Investments [Member]        
Debt Securities, Available-for-sale [Line Items]        
Available-for-sale Securities, Gross Realized Gains $ 0 $ 1,200,000 $ 1,200,000