Other comprehensive income (loss) - Disclosure of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Foreign Currency Translation
Beginning Balance	$ (71,254)	$ (56,783)
Other comprehensive income (loss) before reclassifications	569	(1,818)
Net change	569	(1,818)
Ending Balance	(70,685)	(58,601)
Adjustment of pension and postretirement benefit plans
Beginning Balance	(195,056)	(202,816)
Amounts reclassified from accumulated other comprehensive income (loss) for amortization of net losses	3,242	3,351
Net change	3,242	3,351
Ending Balance	(191,814)	(199,465)
Unrealized net holding gains (losses) on debt securities
Beginning Balance	460,900	92,155
Other comprehensive (loss) income before reclassifications	(369,945)	381,776
Net change	(369,945)	381,776
Ending Balance	90,955	473,931
Unrealized net (losses) gain on cash flow hedges
Beginning Balance	(4,599)	(2,494)
Other comprehensive income (loss) before reclassification	1,357	(3,589)
Amounts reclassified from other accumulated other comprehensive income (loss)	48	841
Net change	1,405	(2,748)
Ending Balance	(3,194)	(5,242)
Accumulated other comprehensive (loss) income	$ (174,738)	$ 210,623	$ 189,991