Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, Net	$ 1,100		$ 1,100
Operating Revenue	139,536	$ 156,695
Revenue from Contract with Customer, Including Assessed Tax	2,800	4,300
fuel surcharge [Member]
Disaggregation of Revenue [Line Items]
Fuel surcharge revenue	$ 17,000	$ 21,500