Workers' Compensation Expense (Worker's Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Total workers' compensation expense
Accrued Workers' Compensation [Line Items]
Total workers' compensation expense	$ 4,863	$ 5,455
Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	1,498	1,949
Interest cost	1,152	1,110
Net amortization	(157)	(591)
Net benefit (credit) cost	2,807	3,650
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 2,056	$ 1,805