Retirement plans - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
TRP
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	$ 70,300,000
Cash contributions	3,700,000	$ 0
TRP | Accrued Liabilities
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	5,900,000
SERP
Defined Benefit Plan Disclosure [Line Items]
Cash contributions	2,800,000	$ 2,800,000
Additional cash payments	$ 900,000