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Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance $ 4,993,223 $ 4,771,240 $ 4,516,193
Net current-period other comprehensive income (loss), net of tax 84,976 35,778 73,051
Ending Balance 5,495,983 4,993,223 4,771,240
Defined Benefit Pension Item [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance (9,645)    
Other comprehensive income (loss) before reclassification 0    
Amounts reclassified from accumulated other comprehensive income 5,447    
Net current-period other comprehensive income (loss), net of tax 5,447    
Ending Balance (4,198) (9,645)  
Unrealized Gains/Losses on AFS Securities [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance (247,964)    
Other comprehensive income (loss) before reclassification 89,466    
Amounts reclassified from accumulated other comprehensive income 0    
Net current-period other comprehensive income (loss), net of tax 89,466    
Ending Balance (158,498) (247,964)  
Accumulated Other Comprehensive Income (Loss) [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance (223,903) (259,681) (332,732)
Other comprehensive income (loss) before reclassification 86,924    
Amounts reclassified from accumulated other comprehensive income (1,948)    
Net current-period other comprehensive income (loss), net of tax 84,976 35,778 73,051
Ending Balance (138,927) (223,903) $ (259,681)
Unrealized Gains/Losses on Cash Flow Hedges [Member]      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Beginning Balance 33,706    
Other comprehensive income (loss) before reclassification (2,542)    
Amounts reclassified from accumulated other comprehensive income (7,395)    
Net current-period other comprehensive income (loss), net of tax (9,937)    
Ending Balance $ 23,769 $ 33,706