Workers Compensation Expense - Worker's compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Total workers' compensation expense
Accrued Workers' Compensation [Line Items]
Total workers' compensation expense	$ 3,953	$ 4,863
Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	993	1,498
Interest cost	1,511	1,152
Net amortization	241	(157)
Net benefit credit	2,263	2,807
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 1,690	$ 2,056