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
	Mar. 31, 2023	Mar. 31, 2022
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net of tax	$ (36,615)	$ (2,111)
Pension and postretirement benefit plan
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(4,813)	(3,911)
Income tax benefit	1,805	1,467
Net of tax	(3,008)	(2,444)
Pension and postretirement benefit plan | Other operating income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(4,813)	(3,911)
Gains (losses) on debt securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(42,040)	0
Income tax benefit	8,407	0
Net of tax	(33,633)	0
Gains (losses) on debt securities | Investment securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(42,040)	0
Cash flow hedge
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	41	699
Income tax benefit	(15)	(366)
Net of tax	26	333
Cash flow hedge | Forward contracts | Mortgage banking activities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	41	978
Cash flow hedge | Interest rate swap | Other operating income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	$ 0	$ (279)