Workers Compensation Expense - Worker's compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Total workers' compensation expense
Accrued Workers' Compensation [Line Items]
Total workers' compensation expense	$ (4,571)	$ 5,026	$ 4,385	$ 14,846
Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	993	1,498	2,980	4,493
Interest cost	1,511	1,153	4,531	3,458
Net amortization	241	(157)	723	(471)
Net benefit credit	2,263	2,808	6,788	8,422
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ (6,834)	$ 2,218	$ (2,403)	$ 6,424