Retirement plans - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
TRP
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	$ 79,100,000
Cash contributions	0	$ 0
Mandatory payment	0
TRP | Accrued liabilities
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	5,600,000
SERP
Defined Benefit Plan Disclosure [Line Items]
Cash contributions	900,000	$ 900,000
Additional cash payments	$ 4,600,000