Retirement plans - Schedule of Net Funded Status (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 386,108
Benefit Obligation	462,466
Funded Status	(76,358)
Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	386,108	$ 385,005	$ 541,758
Benefit Obligation	462,466	464,309	$ 605,834
Funded Status	(76,358)	$ (79,304)
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	0
Benefit Obligation	47,128
Funded Status	(47,128)
All other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	0
Benefit Obligation	297
Funded Status	(297)
TRP | Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	386,108
Benefit Obligation	415,041
Funded Status	$ (28,933)