Workers' Compensation Expense (Narrative) (Details) $ in Millions	1 Months Ended	12 Months Ended
	Feb. 29, 2020 USD ($)	Dec. 31, 2020 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Additional collateral amount	$ 71.1
Number of days required to submit additional collateral to retain self-insurance status	30 days
Increase (decrease) in workers compensation obligations due to change in discount rate		$ 27.6
Reimbursable liabilities		14.3
Insurance receivable, current		0.5
Insurance receivable, noncurrent		13.8
Total workers' compensation expense
Defined Benefit Plan Disclosure [Line Items]
Surety bonds and letters of credit outstanding		$ 122.9
Risk Free Interest Rate | Total workers' compensation expense
Defined Benefit Plan Disclosure [Line Items]
Discount rate		0.0084