v3.26.1
Comprehensive Income/(Loss) - Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance $ 4,070,608 $ 3,781,579 $ 4,031,913 $ 2,790,281
Amounts reclassified from accumulated other comprehensive income (loss) (552) (364) (1,049) (579)
Total other comprehensive (loss) income (5,962) 17,066 (19,837) 44,988
Ending Balance 4,109,685 3,819,220 4,109,685 3,819,220
Accumulated Defined Benefit Plans Adjustment [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     6,584 5,124
Other comprehensive income (loss) before reclassifications     0 0
Amounts reclassified from accumulated other comprehensive income (loss) (231) (148) (458) (275)
Total other comprehensive (loss) income     (458) (275)
Ending Balance 6,126 4,849 6,126 4,849
Accumulated Unrealized Gains (Losses) on Debt Securities Available for Sale [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance     (139,904) (223,756)
Other comprehensive income (loss) before reclassifications     (18,788) 45,567
Amounts reclassified from accumulated other comprehensive income (loss) (321) (216) (591) (304)
Total other comprehensive (loss) income     (19,379) 45,263
Ending Balance (159,283) (178,493) (159,283) (178,493)
Accumulated Other Comprehensive Income (Loss) [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Beginning Balance (147,195) (190,710) (133,320) (218,632)
Other comprehensive income (loss) before reclassifications     (18,788) 45,567
Amounts reclassified from accumulated other comprehensive income (loss)     (1,049) (579)
Total other comprehensive (loss) income (5,962) 17,066 (19,837) 44,988
Ending Balance $ (153,157) $ (173,644) $ (153,157) $ (173,644)