Other comprehensive income (loss) - Reclassification out of accumulated other comprehensive income (Details) - Reclassification out of accumulated other comprehensive income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net of tax	$ (42,677)	$ (14,534)	$ (17,665)
Pension and postretirement benefit plan
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(15,644)	(20,749)	(21,447)
Income tax benefit	5,867	7,781	8,042
Net of tax	(9,777)	(12,968)	(13,405)
Pension and postretirement benefit plan | Other operating expenses
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(15,644)	(20,749)	(21,447)
Gains (losses) on debt securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(41,642)	23	41
Income tax benefit	8,328	(5)	(6)
Net of tax	(33,314)	18	35
Gains (losses) on debt securities | Investment securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(41,642)	0	0
Gains (losses) on debt securities | Net gain (loss) on sale of debt securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	0	23	41
Cash flow hedge
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	960	(1,847)	(6,379)
Income tax benefit	(546)	263	2,084
Net of tax	414	(1,584)	(4,295)
Cash flow hedge | Forward contracts | Mortgage banking activities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	1,458	(704)	(5,559)
Cash flow hedge | Interest rate swap | Other operating expenses
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	$ (498)	$ (1,143)	$ (820)