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Available for Sale Securities - Summary of Gross Unrealized Losses on Securities Available-for-sale and Fair Values (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]    
Fair Value $ 9,219 $ 20,276
Unrealized Loss (23) (138)
Fair Value 638 17,485
Unrealized Loss (7) (258)
Fair Value 9,857 37,761
Unrealized Loss (30) (396)
US States and Political Subdivisions Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 4,235 2,052
Unrealized Loss (11) (14)
Fair Value   667
Unrealized Loss   (6)
Fair Value 4,235 2,719
Unrealized Loss (11) (20)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]    
Debt Securities, Available-for-sale [Line Items]    
Fair Value 4,984 15,830
Unrealized Loss (12) (106)
Fair Value   16,747
Unrealized Loss   (251)
Fair Value 4,984 32,577
Unrealized Loss (12) (357)
Asset-backed Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Fair Value   2,394
Unrealized Loss   (18)
Fair Value 638 71
Unrealized Loss (7) (1)
Fair Value 638 2,465
Unrealized Loss $ (7) $ (19)