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Securities - Amortized Cost and Fair Value of Debt Securities, by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, One year or less	$ 8,867
Amortized Cost, After one year through five years	120,220
Amortized Cost, After five years through ten years	171,484
Amortized Cost, After ten years	349
Amortized Cost, Total	300,920
Amortized Cost, Mortgage-backed securities	124,658
Amortized Cost	425,578	$ 300,602
Fair Value, One year or less	8,923
Fair Value, After one year through five years	121,121
Fair Value, After five years through ten years	171,215
Fair Value, After ten years	359
Fair Value, Total	301,618
Fair Value, Mortgage-backed securities	125,099
Total, Fair Value	$ 426,717	$ 307,812

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