Retirement plans - Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Retirement Benefits [Abstract]
Service cost-benefits earned during the period	$ 0	$ 1	$ 0	$ 2
Interest cost on benefit obligation	4,270	3,969	12,811	11,907
Expected return on plan assets	(4,876)	(8,670)	(14,627)	(26,010)
Amortization of prior service (credit) cost	(119)	23	(361)	68
Amortization of actuarial loss	1,150	1,223	3,452	3,669
Pension payment timing related charge	0	946	0	946
Expense (income) from company-sponsored retirement plans	$ 425	$ (2,508)	$ 1,275	$ (9,418)