Other comprehensive income (loss) - Change in accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Foreign Currency Translation
Beginning Balance	$ (56,735)	$ (67,307)
Other comprehensive loss	(5,245)	(2,858)
Net change	(5,245)	(2,858)
Ending Balance	(61,980)	(70,165)
Adjustment of pension and postretirement benefit plans
Beginning Balance	(144,335)	(158,994)
Other comprehensive income (loss) before reclassification	0	1,269
Amounts reclassified from accumulated other comprehensive loss for amortization of net losses	3,008	2,444
Net change	3,008	3,713
Ending Balance	(141,327)	(155,281)
Unrealized net holding losses on debt securities
Beginning Balance	(2,323,903)	(96,120)
Other comprehensive (loss) income before reclassifications	191,752	(1,075,830)
Amounts reclassified from accumulated other comprehensive loss for amortization of net unrealized losses of debt securities transferred from available-for-sale to held-to-maturity	33,633	0
Net change	225,385	(1,075,830)
Ending Balance	(2,098,518)	(1,171,950)
Unrealized net gains (losses) on cash flow hedges
Beginning Balance	45	(2,648)
Other comprehensive (loss) income before reclassifications	(19)	3,139
Amounts reclassified from accumulated other comprehensive gains	(26)	(333)
Net change	(45)	2,806
Ending Balance	0	158
Accumulated other comprehensive loss, net of tax	$ (2,301,825)	$ (1,397,238)	$ (2,524,928)