Other comprehensive income (loss) - Change in accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Foreign Currency Translation
Beginning Balance	$ (67,307)	$ (71,254)	$ (56,783)
Other comprehensive income	10,572	3,947	(14,471)
Net change	10,572	3,947	(14,471)
Ending Balance	(56,735)	(67,307)	(71,254)
Adjustment of pension and postretirement benefit plans
Beginning Balance	(158,994)	(195,056)	(202,816)
Other comprehensive income (loss) before reclassification	4,882	23,094	(5,645)
Amounts reclassified from accumulated other comprehensive loss for amortization of net losses	9,777	12,968	13,405
Net change	14,659	36,062	7,760
Ending Balance	(144,335)	(158,994)	(195,056)
Unrealized net holding (losses) gains on debt securities
Beginning Balance	(96,120)	460,900	92,155
Other comprehensive (loss) income	(2,261,097)	(557,002)	368,780
Amounts reclassified from accumulated other comprehensive (loss) income for gains on securities	0	(18)	(35)
Amounts reclassified from accumulated other comprehensive (loss) income for amortization of net unrealized losses of debt securities transferred from available-for-sale to held-to-maturity	33,314	0	0
Net change	(2,227,783)	(557,020)	368,745
Ending Balance	(2,323,903)	(96,120)	460,900
Unrealized net gains (losses) on cash flow hedges
Beginning Balance	(2,648)	(4,599)	(2,494)
Other comprehensive income (loss) before reclassifications	3,107	367	(6,400)
Amounts reclassified from accumulated other comprehensive income (loss)	(414)	1,584	4,295
Net change	2,693	1,951	(2,105)
Ending Balance	45	(2,648)	(4,599)
Accumulated other comprehensive loss, net of tax	$ (2,524,928)	$ (325,069)	$ 189,991	$ 189,991