Note 11 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating revenue	$ 279,538	$ 324,448	$ 863,233	$ 941,294
Operating income	17,230	33,766	74,453	110,561
Truckload [Member]
Operating revenue	114,227	129,376	351,991	369,138
Operating income	2,738	14,319	22,348	45,978
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	96,516	105,905	300,104	302,883
Truckload [Member] | Truckload Fuel Surcharge Revenue [Member]
Operating revenue	17,711	23,471	51,887	66,255
Dedicated [Member]
Operating revenue	101,797	110,217	313,231	317,332
Operating income	11,286	13,005	39,143	37,689
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	82,963	86,178	257,231	248,988
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	18,834	24,039	56,000	68,344
Intermodal [Member]
Operating revenue	22,047	31,903	73,001	100,512
Operating income	(1,074)	778	(452)	9,911
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	18,122	24,303	60,277	77,589
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	3,925	7,600	12,724	22,923
Brokerage [Member]
Operating revenue	41,467	52,952	125,010	154,312
Operating income	$ 4,280	$ 5,664	$ 13,414	$ 16,983