Note 16 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating revenue	$ 973,644	$ 874,374	$ 843,271
Operating Income	111,689	93,246	76,498
Truckload [Member]
Operating revenue	396,666	379,148	378,000
Operating Income	51,032	39,637	29,666
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	346,289	342,357	329,304
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	50,377	36,791	48,696
Dedicated [Member]
Operating revenue	329,442	309,784	265,984
Operating Income	36,395	40,909	31,245
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	276,883	271,550	223,935
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	52,559	38,234	42,049
Intermodal [Member]
Operating revenue	102,245	88,733	90,394
Operating Income	9,479	5,730	6,612
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	87,468	79,944	77,750
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	14,777	8,789	12,644
Brokerage [Member]
Operating revenue	145,291	96,709	108,893
Operating Income	$ 14,783	$ 6,970	$ 8,975