Workers Compensation Expense (Worker's Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Total workers' compensation expense
Accrued Workers' Compensation [Line Items]
Total workers' compensation expense	$ 4,956	$ 5,515	$ 9,819	$ 10,969
Occupational disease
Accrued Workers' Compensation [Line Items]
Service cost	1,497	1,949	2,995	3,898
Interest cost	1,152	1,111	2,304	2,220
Net amortization	(157)	(590)	(314)	(1,181)
Net benefit (credit) cost	2,806	3,650	5,613	7,299
Traumatic injury claims and assessments
Accrued Workers' Compensation [Line Items]
Traumatic injury claims and assessments	$ 2,150	$ 1,865	$ 4,206	$ 3,670