Retirement plans - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
TRP
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	$ 59,100,000
Cash contributions	0	$ 0
TRP | Accrued liabilities
Defined Benefit Plan Disclosure [Line Items]
Total net pension obligations	6,000,000
SERP
Defined Benefit Plan Disclosure [Line Items]
Cash contributions	2,900,000	$ 5,300,000
Additional cash payments	$ 2,500,000