Note 15 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Operating revenue	$ 1,263,878	$ 973,644	$ 874,374
Operating income:
Operating Income	143,344	111,689	93,246
Truckload [Member]
Operating revenue	500,462	396,666	379,148
Operating income:
Operating Income	59,392	51,032	39,637
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	411,448	346,289	342,357
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	89,014	50,377	36,791
Dedicated [Member]
Operating revenue	429,092	329,442	309,784
Operating income:
Operating Income	50,566	36,395	40,909
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	336,973	276,883	271,550
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	92,119	52,559	38,234
Intermodal [Member]
Operating revenue	129,765	102,245	88,733
Operating income:
Operating Income	10,639	9,479	5,730
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	100,452	87,468	79,944
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	29,313	14,777	8,789
Brokerage [Member]
Operating revenue	204,559	145,291	96,709
Operating income:
Operating Income	$ 22,747	$ 14,783	$ 6,970