Note 14 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating revenue	$ 1,131,455	$ 1,263,878	$ 973,644
Operating income/(loss):
Operating Income	90,110	143,344	111,689
Truckload [Member]
Operating revenue	465,475	500,462	396,666
Operating income/(loss):
Operating Income	24,835	59,392	51,032
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	395,565	411,448	346,289
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	69,910	89,014	50,377
Dedicated [Member]
Operating revenue	408,272	429,092	329,442
Operating income/(loss):
Operating Income	48,377	50,566	36,395
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	334,962	336,973	276,883
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	73,310	92,119	52,559
Intermodal [Member]
Operating revenue	92,078	129,765	102,245
Operating income/(loss):
Operating Income	(156)	10,639	9,479
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	75,887	100,452	87,468
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	16,191	29,313	14,777
Brokerage [Member]
Operating revenue	165,630	204,559	145,291
Operating income/(loss):
Operating Income	$ 17,054	$ 22,747	$ 14,783