Workers' Compensation Expense (Occupational Disease Costs Activity and Assumptions) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Self Insurance Reserve [Roll Forward]
Service cost	$ 7,796	$ 7,564	$ 6,677
Interest cost	$ 4,439	$ 5,115	4,922
Discount Rate
Self Insurance Reserve [Roll Forward]
Discount rate	0.0282	0.0248
Occupational disease
Self Insurance Reserve [Roll Forward]
Beginning of period	$ 183,001	$ 158,325
Service cost	7,796	7,564
Interest cost	4,439	5,115
Actuarial (gain) loss	(21,245)	19,327
Benefit and administrative payments	(6,406)	(7,330)
End of period	$ 167,585	$ 183,001	$ 158,325