v3.26.1
Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Net of Tax        
Balance at beginning of year $ 2,767,760 $ 2,648,852 $ 2,769,365 $ 2,617,486
Other comprehensive income (loss) 12,954 26,761 8,347 56,986
Balance at end of period 2,826,028 2,694,545 2,826,028 2,694,545
Accumulated Other Comprehensive Income (Loss)        
Net of Tax        
Balance at beginning of year (372,747) (433,769) (368,140) (463,994)
Other comprehensive income (loss) 12,954 26,761 8,347 56,986
Balance at end of period (359,793) (407,008) (359,793) (407,008)
Pensions and Other Benefits        
Net of Tax        
Balance at beginning of year (4,290) (1,879) (4,290) (1,879)
Balance at end of period (4,290) (1,879) (4,290) (1,879)
Investment securities        
Net of Tax        
Other comprehensive income (loss) 14,191 26,643 9,505 56,695
Available-for-Sale Investment Securities        
Net of Tax        
Balance at beginning of year (139,895) (170,558) (125,007) (193,529)
Other comprehensive income (loss) 7,075 19,324 (7,813) 42,295
Balance at end of period (132,820) (151,234) (132,820) (151,234)
Held-to-Maturity Investment Securities        
Net of Tax        
Balance at beginning of year (228,098) (261,420) (238,300) (268,501)
Other comprehensive income (loss) 7,116 7,319 17,318 14,400
Balance at end of period (220,982) (254,101) (220,982) (254,101)
Cash Flow Derivative Hedges        
Net of Tax        
Balance at beginning of year (464) 88 (543) (85)
Other comprehensive income (loss) (1,237) 118 (1,158) 291
Balance at end of period $ (1,701) $ 206 $ (1,701) $ 206