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		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification out of accumulated other comprehensive loss
Net of tax	$ (1,976)	$ (3,524)	$ (4,087)	$ (6,814)
Pension and postretirement benefit plan
Reclassification out of accumulated other comprehensive loss
Before Tax	(3,911)	(5,189)	(7,822)	(10,379)
Income tax benefit	1,467	1,947	2,934	3,895
Net of tax	(2,444)	(3,242)	(4,888)	(6,484)
Pension and postretirement benefit plan | Other operating income
Reclassification out of accumulated other comprehensive loss
Before Tax	(3,911)	(5,189)	(7,822)	(10,379)
Cash flow hedge
Reclassification out of accumulated other comprehensive loss
Before Tax	880	(280)	1,579	(189)
Income tax benefit	(412)	(2)	(778)	(141)
Net of tax	468	(282)	801	(330)
Cash flow hedge | Forward contracts | Mortgage banking activities
Reclassification out of accumulated other comprehensive loss
Before Tax	1,099	2	2,077	348
Cash flow hedge | Interest rate swap | Other operating income
Reclassification out of accumulated other comprehensive loss
Before Tax	$ (219)	$ (282)	$ (498)	$ (537)