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Investment Securities - Additional Information (Detail) - USD ($)
9 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]    
Total deposits $ 12,358,786,000 $ 12,836,245,000
Debt securities, held-to-maturity, allowance for credit loss 0 0
Investment in FHLB stock, impairment losses $ 0  
Debt securities weighted average remaining contractual maturity term 23 years  
United States [Member]    
Debt Securities, Available-for-sale [Line Items]    
Securities issued by U.S. government percentage 91.00%  
Investment Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Pledged to secure amount $ 2,160,000,000 1,560,000,000
Total deposits 1,340,000,000 1,130,000,000
Secure public funds 433,500,000 652,000,000
Outstanding borrowings 870,000,000 550,000,000
Other purposes 52,000,000 27,000
Pledged to secure unused borrowing capacity 2,940,000,000 3,150,000,000
Secured unused borrowing capacity $ 1,580,000,000 $ 105,000,000