Other comprehensive income (loss) - Reclassification out of accumulated other comprehensive income (Details) - Reclassification out of accumulated other comprehensive loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification out of accumulated other comprehensive loss
Net of tax	$ (38,036)	$ (2,962)	$ (111,981)	$ (7,049)
Pension and postretirement benefit plan
Reclassification out of accumulated other comprehensive loss
Before Tax	(4,814)	(3,911)	(14,440)	(11,733)
Income tax benefit	1,805	1,467	5,415	4,401
Net of tax	(3,009)	(2,444)	(9,025)	(7,332)
Pension and postretirement benefit plan | Other operating income (expenses)
Reclassification out of accumulated other comprehensive loss
Before Tax	(4,814)	(3,911)	(14,440)	(11,733)
Unrealized holding losses on debt securities
Reclassification out of accumulated other comprehensive loss
Before Tax	(43,783)	0	(128,726)	0
Income tax benefit	8,756	0	25,744	0
Net of tax	(35,027)	0	(102,982)	0
Unrealized holding losses on debt securities | Investment securities
Reclassification out of accumulated other comprehensive loss
Before Tax	(43,783)	0	(128,726)	0
Cash flow hedge
Reclassification out of accumulated other comprehensive loss
Before Tax	0	(828)	41	751
Income tax benefit	0	310	(15)	(468)
Net of tax	0	(518)	26	283
Cash flow hedge | Forward contracts | Mortgage banking activities
Reclassification out of accumulated other comprehensive loss
Before Tax	0	(609)	41	1,249
Cash flow hedge | Interest rate swap | Other operating income (expenses)
Reclassification out of accumulated other comprehensive loss
Before Tax	$ 0	$ (219)	$ 0	$ (498)