v3.26.3
Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Jun. 30, 2026
Mar. 31, 2026
Sep. 30, 2025
Jun. 30, 2025
Mar. 31, 2025
Sep. 30, 2026
Sep. 30, 2025
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Beginning Balance $ 5,510,537 $ 5,488,126 $ 5,495,983 $ 5,364,541 $ 5,314,449 $ 4,993,223 $ 5,495,983 $ 4,993,223
Total change in other comprehensive income, net of tax (79,670) 5,748 (10,188) 25,913 11,280 28,895 (84,110) 66,088
Ending Balance 5,413,913 5,510,537 5,488,126 5,445,715 5,364,541 5,314,449 5,413,913 5,445,715
Defined Benefit Pension Item [Member]                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Beginning Balance     (4,198)       (4,198)  
Other comprehensive (loss) income before reclassification             0  
Amounts reclassified from accumulated other comprehensive income             0  
Total change in other comprehensive income, net of tax             0  
Ending Balance (4,198)           (4,198)  
Unrealized Gains/Losses on AFS Securities [Member]                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Beginning Balance     (158,498)       (158,498)  
Other comprehensive (loss) income before reclassification             (95,939)  
Amounts reclassified from accumulated other comprehensive income             7,403  
Total change in other comprehensive income, net of tax             (88,536)  
Ending Balance (247,034)           (247,034)  
Unrealized Gains/Losses on Cash Flow Hedges [Member]                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Beginning Balance     23,769       23,769  
Other comprehensive (loss) income before reclassification             9,032  
Amounts reclassified from accumulated other comprehensive income             (4,606)  
Total change in other comprehensive income, net of tax             4,426  
Ending Balance 28,195           28,195  
Accumulated Other Comprehensive Income (Loss) [Member]                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Beginning Balance (143,367) (149,115) (138,927) (183,728) (195,008) (223,903) (138,927) (223,903)
Other comprehensive (loss) income before reclassification             (86,907)  
Amounts reclassified from accumulated other comprehensive income             2,797  
Total change in other comprehensive income, net of tax (79,670) 5,748 (10,188) 25,913 11,280 28,895 (84,110)  
Ending Balance $ (223,037) $ (143,367) $ (149,115) $ (157,815) $ (183,728) $ (195,008) $ (223,037) $ (157,815)