Other comprehensive income (loss) - Reclassification out of accumulated other comprehensive income (Details) - Reclassification out of accumulated other comprehensive income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification out of accumulated other comprehensive loss
Net of tax	$ (2,962)	$ (4,282)	$ (7,049)	$ (11,096)
Pension and postretirement benefit plan
Reclassification out of accumulated other comprehensive loss
Before Tax	(3,911)	(5,187)	(11,733)	(15,566)
Income tax benefit	1,467	1,945	4,401	5,840
Net of tax	(2,444)	(3,242)	(7,332)	(9,726)
Pension and postretirement benefit plan | Other operating income
Reclassification out of accumulated other comprehensive loss
Before Tax	(3,911)	(5,187)	(11,733)	(15,566)
Gains (losses) on debt securities
Reclassification out of accumulated other comprehensive loss
Before Tax	0	23	0	23
Income tax benefit	0	(5)	0	(5)
Net of tax	0	18	0	18
Gains (losses) on debt securities | Net gain (loss) on sale of debt securities
Reclassification out of accumulated other comprehensive loss
Before Tax	0	23	0	23
Cash flow hedge
Reclassification out of accumulated other comprehensive loss
Before Tax	(828)	(1,518)	751	(1,707)
Income tax benefit	310	460	(468)	319
Net of tax	(518)	(1,058)	283	(1,388)
Cash flow hedge | Forward contracts | Mortgage banking activities
Reclassification out of accumulated other comprehensive loss
Before Tax	(828)	(1,229)	1,249	(854)
Cash flow hedge | Interest rate swap | Other operating income
Reclassification out of accumulated other comprehensive loss
Before Tax	$ 0	$ (289)	$ (498)	$ (853)