Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Line items]
Allowance for doubtful accounts	$ 11,400,000	$ 11,100,000
Rerate reserve as a reduction to accounts receivable	7,900,000	12,500,000
Deferred revenue	$ 25,200,000	$ 25,700,000
Risk-free rate for maturities of workers' compensation claims	2.00%	2.60%	1.50%
Risk-free rate for property damage and liability claims	2.10%	2.50%	1.30%
Depreciation	$ 150,500,000	$ 145,900,000	$ 147,700,000
Restricted amounts held in escrow-current	0	0
Cargo Claims And Other Insurance Related Amounts
Accounting Policies [Line items]
Undiscounted amount	$ 13,700,000	$ 13,900,000
Workforce Subject to Collective Bargaining Arrangements | Labor Force Concentration Risk
Accounting Policies [Line items]
Percentage of workforce subject to collective bargaining agreements	79.00%