Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract with Customer, Asset, after Allowance for Credit Loss	$ 1,400		$ 1,400		$ 1,200
Operating Revenue	160,873	$ 142,144	327,191	$ 281,681
Revenue from Contract with Customer, Including Assessed Tax	3,400	2,700	6,900	5,500
fuel surcharge [Member]
Disaggregation of Revenue [Line Items]
Fuel surcharge revenue	$ 14,000	$ 18,100	$ 33,400	$ 35,100