Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Contract with Customer, Asset, Net [Abstract]
Contract with Customer, Asset, Net	$ 1,300	$ 1,100
Operating Revenues	607,300	645,300	$ 596,800
Fuel surcharge revenue	76,100	61,700	75,000
Accessorial and other revenues	11,400	14,300	$ 13,500
Deposit Contracts, Liabilities	$ 0	$ 0