Workers Compensation Expense - Worker's compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Total workers' compensation expense
Accrued Workers' Compensation [Line Items]
Total workers' compensation expense	$ 5,026	$ 5,428	$ 14,846	$ 16,398
Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	1,498	1,949	4,493	5,847
Interest cost	1,153	1,110	3,458	3,330
Net amortization	(157)	(590)	(471)	(1,772)
Net benefit (credit) cost	2,808	3,649	8,422	10,949
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 2,218	$ 1,779	$ 6,424	$ 5,449