Shareholders' equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 2,519,906
Other comprehensive (loss) gain before reclassifications	(16,211)	$ 19,287	$ 16,881
Amounts reclassified from AOCL	(12,106)	4,573	4,640
Ending Balance	3,071,722	2,519,906
Retirement Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(113,090)	(120,979)	(142,398)
Other comprehensive (loss) gain before reclassifications	(16,288)	3,316	16,779
Amounts reclassified from AOCL	3,313	4,573	4,640
Ending Balance	(126,065)	(113,090)	(120,979)
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	455	(97)	(199)
Other comprehensive (loss) gain before reclassifications	77	552	102
Amounts reclassified from AOCL	0	0	0
Ending Balance	532	455	(97)
Available-For-Sale Investment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	15,419	0
Other comprehensive (loss) gain before reclassifications	0	15,419
Amounts reclassified from AOCL	(15,419)	0
Ending Balance	0	15,419	0
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(97,216)	(121,076)	(142,597)
Ending Balance	$ (125,533)	$ (97,216)	$ (121,076)