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Financial Instruments with Off-Balance-Sheet Risk - Narrative (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Jan. 01, 2020
Dec. 31, 2019
Loss Contingencies [Line Items]      
Allowance for credit losses on lending-related commitments $ 2,300   $ 49
Lending-related commitments, benefit $ 1,100    
Cumulative Effect, Period of Adoption, Adjustment      
Loss Contingencies [Line Items]      
Allowance for credit losses on lending-related commitments   $ 3,388