Pension and postretirement benefits - Contributions to the benefit plans (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Dec. 31, 2022
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Employer contribution	$ 170
Expected future employer contribution current year		$ 227
OPEB Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Employer contribution	$ 5,046
Expected future employer contribution current year		$ 5,971