Accumulated other comprehensive loss - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 2,704,872
Beginning balance	$ 2,797,889	$ 3,151,265	2,704,872	$ 3,071,722
Amounts reclassified from AOCL	1,110	988	2,221	2,066
Other comprehensive income, net of tax	1,110	988	2,221	2,066
Ending balance	2,801,100	2,904,158	2,801,100	2,904,158
Ending Balance	2,801,100		2,801,100
Total
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(118,499)	(124,455)	(119,610)	(125,533)
Beginning balance	(118,499)	(124,455)	(119,610)	(125,533)
Amounts reclassified from AOCL	1,110	988	2,221	2,066
Other comprehensive income, net of tax	1,110	988	2,221	2,066
Ending balance	(117,389)	(123,467)	(117,389)	(123,467)
Ending Balance	(117,389)	(123,467)	(117,389)	(123,467)
Retirement Plans
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(119,031)	(124,987)	(120,142)	(126,065)
Amounts reclassified from AOCL	1,110	988	2,221	2,066
Other comprehensive income, net of tax	1,110	988	2,221	2,066
Ending balance	(117,921)	(123,999)	(117,921)	(123,999)
Foreign Currency
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	532	532	532	532
Amounts reclassified from AOCL
Other comprehensive income, net of tax
Ending Balance	$ 532	$ 532	$ 532	$ 532