Retirement plans - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
TRP
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	$ 75,500,000
Cash contributions	0	$ 0
Expected cash payments	6,900,000
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	900,000	$ 900,000
Additional cash payments	$ 4,900,000