Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Contract with Customer, Asset, Net [Abstract]
Contract with Customer, Asset, Net	$ 1,200	$ 1,100
Operating Revenues	596,800	610,800	$ 607,300
Fuel surcharge revenue	75,000	85,300	72,500
Revenue from Contract with Customer, Including Assessed Tax	13,500	14,900	$ 24,300
Deposit Contracts, Liabilities	$ 0	$ 0