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Fair Value of Financial Instruments - Summary of Carrying Values and Fair Values of Financial Instruments (Parenthetical) (Detail) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Interest-bearing funds deposited in other banks $ 1,500,000  
Publicly traded retail notes traded at a premium to par 336,000 $ 1,681,000
Fair Value Recurring [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Interest-bearing funds deposited in other banks 1,500,000  
Fair Value Recurring [Member] | Level 2 [Member]    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Interest-bearing funds deposited in other banks $ 1,500,000