Note 11 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues	$ 298,023	$ 287,281
Operating income:
Operating income	29,010	35,858
Truckload [Member]
Revenues	120,626	112,790
Operating income:
Operating income	10,041	15,571
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Revenues	102,320	95,170
Truckload [Member] | Fuel Surcharge Revenue [Member]
Revenues	18,306	17,620
Dedicated [Member]
Revenues	106,449	96,760
Operating income:
Operating income	13,684	10,645
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Revenues	86,831	78,421
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Revenues	19,618	18,339
Intermodal [Member]
Revenues	28,589	31,642
Operating income:
Operating income	787	5,036
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Revenues	23,401	25,605
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Revenues	5,188	6,037
Brokerage [Member]
Revenues	42,359	46,089
Operating income:
Operating income	$ 4,498	$ 4,606