Accumulated other comprehensive loss - Reclassifications out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ (19,825)	$ 1,225
Income tax effect	5,130	(316)
Total reclassifications, net of tax	(14,695)	909
Amortization of prior service (credit) cost, net
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	(125)	25
Amortization of actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	1,100	1,200
Realized gain on available-for-sale investment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications, before tax	$ (20,800)	$ 0