Workers' Compensation Expense (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Reimbursable liabilities	$ 20.3
Insurance receivable, current	3.3
Insurance receivable, noncurrent	17.0
Traumatic and other workers’ compensation claims
Defined Benefit Plan Disclosure [Line Items]
Surety bonds and letters of credit outstanding	$ 121.7
Risk Free Interest Rate | Traumatic and other workers’ compensation claims
Defined Benefit Plan Disclosure [Line Items]
Discount rate	0.0308