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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net of tax	$ (37,330)	$ (1,976)	$ (73,945)	$ (4,087)
Pension and postretirement benefit plan
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(4,813)	(3,911)	(9,626)	(7,822)
Income tax benefit	1,805	1,467	3,610	2,934
Net of tax	(3,008)	(2,444)	(6,016)	(4,888)
Pension and postretirement benefit plan | Other operating income (expenses)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(4,813)	(3,911)	(9,626)	(7,822)
Cash flow hedge
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	0	880	41	1,579
Income tax benefit	0	(412)	(15)	(778)
Net of tax	0	468	26	801
Cash flow hedge | Forward contracts | Mortgage banking activities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	0	1,099	41	2,077
Cash flow hedge | Interest rate swap | Other operating income (expenses)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	0	(219)	0	(498)
Unrealized holding losses on debt securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	(42,903)	0	(84,943)	0
Income tax benefit	8,581	0	16,988	0
Net of tax	(34,322)	0	(67,955)	0
Unrealized holding losses on debt securities | Investment securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Before Tax	$ (42,903)	$ 0	$ (84,943)	$ 0