v3.26.1
Investment Securities - Additional Information (Detail)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
Contract
Dec. 31, 2025
USD ($)
Schedule of Investments [Line Items]    
Accrued interest receivable $ 13,608 $ 12,717
Gross unrealized losses on available for sale securities $ 218,489 216,639
Available for sale securities in unrealized loss position | Contract 878  
Available for sale securities in portfolio, number | Contract 1,034  
Capitalization of banks, equal to or greater than, in the single-issue trust preferred portfolio $ 10,000,000  
Equity securities at estimated fair value 30,107 34,760
Carrying value of securities pledged $ 2,063,626 2,102,175
Fitch, AAA Rating [Member]    
Schedule of Investments [Line Items]    
Percentage of asset backed securities with credit rating 23.00%  
Federal Family Education Loan Program [Member] | Fitch, AA+ Rating [Member]    
Schedule of Investments [Line Items]    
Percentage of asset backed securities with credit rating 77.00%  
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 $ 41,938  
Available for sale debt securities 0  
Investment Grade [Member]    
Schedule of Investments [Line Items]    
Amortized cost of available for sale single issue trust preferred securities 7,492  
Unrated Bonds Investment Grade [Member]    
Schedule of Investments [Line Items]    
Amortized cost of available for sale single issue trust preferred securities 5,838  
State and Political Subdivisions [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities $ 55,882 55,634
Percent of portfolio with credit support 46.00%  
Amortized cost of available for sale single issue trust preferred securities $ 564,691  
Agency Mortgage Backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized cost of available for sale single issue trust preferred securities 2,242,507  
Commercial Mortgage-Backed Securities [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 17,722 26,052
Amortized cost of available for sale single issue trust preferred securities 327,174  
Residential Mortgage-Backed Securities, Agency [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 127,368 114,317
Amortized cost of available for sale single issue trust preferred securities 1,915,333  
Residential Mortgage-Backed Securities, Non-agency [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 4,060 4,237
Amortized cost of available for sale single issue trust preferred securities $ 41,938  
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 $ 9,566 11,881
Amortized cost of available for sale single issue trust preferred securities $ 212,504  
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 $ 143,149  
Asset-backed Securities [Member]    
Schedule of Investments [Line Items]    
Gross unrealized losses on available for sale securities 2,121 $ 2,381
Amortized cost of available for sale single issue trust preferred securities $ 175,611