Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, after Allowance for Credit Loss	$ 1,100		$ 1,100		$ 1,200
Operating Revenue	162,282	$ 147,908	489,473	$ 429,589
Revenue from Contract with Customer, Including Assessed Tax	3,600	3,500	10,500	9,100
fuel surcharge [Member]
Disaggregation of Revenue [Line Items]
Fuel surcharge revenue	$ 14,400	$ 18,400	$ 47,900	$ 53,500