Other comprehensive income (loss) - Change in accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Foreign Currency Translation
Beginning Balance	$ (64,167)	$ (67,959)	$ (67,307)	$ (71,254)
Other comprehensive income	7,206	(1,265)	10,346	2,030
Net change	7,206	(1,265)	10,346	2,030
Ending Balance	(56,961)	(69,224)	(56,961)	(69,224)
Adjustment of pension and postretirement benefit plans
Beginning Balance	(152,837)	(188,572)	(158,994)	(195,056)
Other comprehensive income before reclassifications	0	0	1,269	0
Amounts reclassified from accumulated other comprehensive loss for amortization of net losses	2,444	3,242	7,332	9,726
Net change	2,444	3,242	8,601	9,726
Ending Balance	(150,393)	(185,330)	(150,393)	(185,330)
Unrealized net holding (losses) gains on debt securities
Beginning Balance	(1,735,370)	163,982	(96,120)	460,900
Other comprehensive (loss) income	(781,898)	(46,956)	(2,421,148)	(343,874)
Amounts reclassified from accumulated other comprehensive income for gains on securities	0	(18)	0	(18)
Net change	(781,898)	(46,974)	(2,421,148)	(343,892)
Ending Balance	(2,517,268)	117,008	(2,517,268)	117,008
Unrealized net losses on cash flow hedges
Beginning Balance	(642)	(3,142)	(2,648)	(4,599)
Other comprehensive (loss) income before reclassifications	415	(465)	3,222	662
Amounts reclassified from accumulated other comprehensive loss	518	1,058	(283)	1,388
Net change	933	593	2,939	2,050
Ending Balance	291	(2,549)	291	(2,549)
Accumulated other comprehensive loss, net of tax	$ (2,724,331)	$ (140,095)	$ (2,724,331)	$ (140,095)	$ (325,069)