v3.26.1
Other comprehensive income (loss) - Reclassification out of accumulated other comprehensive loss (Details) - Reclassifications Out of Accumulated Other Comprehensive Loss - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Reclassifications Out of Accumulated Other Comprehensive Loss    
Net of tax $ (38,912) $ (37,670)
Adjustment of pension and postretirement benefit plans    
Reclassifications Out of Accumulated Other Comprehensive Loss    
Before Tax (2,258) (2,273)
Income tax benefit (expense) 847 852
Net of tax (1,411) (1,421)
Adjustment of pension and postretirement benefit plans | Other operating expenses    
Reclassifications Out of Accumulated Other Comprehensive Loss    
Before Tax (2,258) (2,273)
Unrealized net holding losses on debt securities    
Reclassifications Out of Accumulated Other Comprehensive Loss    
Before Tax (46,876) (45,311)
Income tax benefit (expense) 9,375 9,062
Net of tax (37,501) (36,249)
Unrealized net holding losses on debt securities | Interest income from investment securities    
Reclassifications Out of Accumulated Other Comprehensive Loss    
Before Tax $ (46,876) $ (45,311)