Note 11 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating revenue	$ 218,646	$ 199,023
Operating Income	18,032	17,733
Truckload [Member]
Operating revenue	95,132	91,722
Operating Income	6,785	7,555
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	83,857	80,167
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	11,275	11,555
Dedicated [Member]
Operating revenue	75,037	57,725
Operating Income	8,533	5,515
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	64,159	48,924
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	10,878	8,801
Intermodal [Member]
Operating revenue	23,680	22,971
Operating Income	1,306	2,394
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	20,594	19,755
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	3,086	3,216
Brokerage [Member]
Operating revenue	24,797	26,605
Operating Income	$ 1,408	$ 2,269