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Investment Securities - Additional Information (Detail)
12 Months Ended
Dec. 31, 2025
USD ($)
Contract
Dec. 31, 2024
USD ($)
Schedule of Investments [Line Items]    
Accrued interest receivable $ 12,717,000 $ 14,776,000
Gross unrealized losses on available for sale securities $ 216,639,000 323,937,000
Available for sale securities in unrealized loss position | Contract 864  
Available for sale securities in portfolio, number | Contract 1,045  
Capitalization of banks, equal to or greater than, in the single-issue trust preferred portfolio $ 10,000,000,000  
Equity securities at estimated fair value 34,760,000 21,058,000
Carrying value of securities pledged 2,102,175,000 2,038,864,000
Held-to-maturity securities amortized cost 1,004,000 1,002,000
Held-to-maturity securities estimated fair value $ 1,020,000 1,020,000
Fitch, AAA Rating [Member]    
Schedule of Investments [Line Items]    
Percentage of asset backed securities with credit rating 36.00%  
Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]    
Schedule of Investments [Line Items]    
Percentage of asset backed securities with credit rating 64.00%  
Minimum [Member] | Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]    
Schedule of Investments [Line Items]    
Percentage of repayment guaranteed by the government 97.00%  
Non Agency Residential Mortgage Backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized cost of available for sale single issue trust preferred securities $ 42,792,000  
Available for sale debt securities $ 0  
Investment Grade [Member]    
Schedule of Investments [Line Items]    
Percentage of asset backed securities with credit rating 99.00%  
Amortized cost of available for sale single issue trust preferred securities $ 7,489,000  
Unrated Bonds Investment Grade [Member]    
Schedule of Investments [Line Items]    
Amortized cost of available for sale single issue trust preferred securities 5,830,000  
State and Political Subdivisions [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities $ 55,634,000 79,515,000
Percent of portfolio with credit support 46.00%  
Amortized cost of available for sale single issue trust preferred securities $ 572,217,000  
Agency Mortgage Backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized cost of available for sale single issue trust preferred securities 1,883,613,000  
Commercial Mortgage-Backed Securities [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 26,052,000 42,698,000
Amortized cost of available for sale single issue trust preferred securities 416,177,000  
Residential Mortgage-Backed Securities, Agency [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 114,317,000 167,114,000
Amortized cost of available for sale single issue trust preferred securities 1,467,436,000  
Residential Mortgage-Backed Securities, Non-agency [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 4,237,000 6,531,000
Amortized cost of available for sale single issue trust preferred securities $ 42,792,000  
Residential Mortgage-Backed Securities, Non-agency [Member] | AAA [Member]    
Schedule of Investments [Line Items]    
Percentage of asset backed securities with credit rating 100.00%  
Corporate Bonds [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities $ 11,881,000 21,571,000
Amortized cost of available for sale single issue trust preferred securities $ 244,244,000  
Corporate Bonds [Member] | Investment Grade [Member]    
Schedule of Investments [Line Items]    
Percent of corporate securities portfolio 95.00%  
Corporate Bonds [Member] | Below Investment Grade [Member]    
Schedule of Investments [Line Items]    
Percent of corporate securities portfolio 2.00%  
Corporate Bonds [Member] | Unrated Bonds Investment Grade [Member]    
Schedule of Investments [Line Items]    
Percent of corporate securities portfolio 3.00%  
Mortgage Backed Securities [Member]    
Schedule of Investments [Line Items]    
Net unrealized gains $ 133,811,000  
Held-to-maturity securities amortized cost 1,926,405,000  
Held-to-maturity securities estimated fair value 1,792,594,000  
Asset-backed Securities [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 2,381,000 $ 2,047,000
Amortized cost of available for sale single issue trust preferred securities 225,617,000  
Asset-backed Securities [Member] | Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]    
Schedule of Investments [Line Items]    
Available for sale debt securities $ 0