Workers' Compensation Expense (Worker's Compensation Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accrued Workers' Compensation [Line Items]
Service cost	$ 7,796	$ 7,564	$ 6,677
Interest cost	4,439	5,115	4,922
Net amortization	2,363	1,189	0
Total workers' compensation expense
Accrued Workers' Compensation [Line Items]
Total workers' compensation expense	18,523	26,790	24,649
Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	7,796	7,564
Interest cost	4,439	5,115
Net benefit cost (credit)	14,598	13,868	11,599
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 3,925	$ 12,922	$ 13,050