Accumulated other comprehensive loss - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 3,004,714
Beginning balance	$ 3,038,870	$ 2,797,889	3,004,714	$ 2,704,872
Amounts reclassified from AOCL	1,089	1,110	2,112	2,221
Other comprehensive income, net of tax	1,089	1,110	2,112	2,221
Ending balance	3,093,323	2,801,100	3,093,323	2,801,100
Ending Balance	3,093,323		3,093,323
Total
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(105,621)	(118,499)	(106,644)	(119,610)
Beginning balance	(105,621)	(118,499)	(106,644)	(119,610)
Amounts reclassified from AOCL	1,089	1,110	2,112	2,221
Other comprehensive income, net of tax	1,089	1,110	2,112	2,221
Ending balance	(104,532)	(117,389)	(104,532)	(117,389)
Ending Balance	(104,532)	(117,389)	(104,532)	(117,389)
Retirement Plans
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(106,153)	(119,031)	(107,176)	(120,142)
Amounts reclassified from AOCL	1,089	1,110	2,112	2,221
Other comprehensive income, net of tax	1,089	1,110	2,112	2,221
Ending balance	(105,064)	(117,921)	(105,064)	(117,921)
Foreign Currency
Increase (Decrease) in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	532	532	532	532
Amounts reclassified from AOCL	0	0	0	0
Other comprehensive income, net of tax	0	0	0	0
Ending Balance	$ 532	$ 532	$ 532	$ 532