Retirement plans - Narrative (Details) - USD ($)	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
TRP
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	$ 73,700,000
Cash contributions	1,000,000	$ 0
Expected additional cash payments	2,800,000
TRP | Accrued Liabilities
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	5,800,000
SERP
Defined Benefit Plan Disclosure [Line Items]
Cash contributions	1,900,000	$ 1,900,000
Additional cash payments	$ 3,000,000