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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Operating revenue	$ 324,448	$ 251,280	$ 941,294	$ 706,768
Operating income:
Operating Income	33,766	28,496	110,561	81,012
Truckload [Member]
Operating revenue	129,376	99,617	369,138	290,473
Operating income:
Operating Income	14,319	11,670	45,978	36,282
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	105,905	86,889	302,883	254,441
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	23,471	12,728	66,255	36,032
Dedicated [Member]
Operating revenue	110,217	82,162	317,332	240,520
Operating income:
Operating Income	13,005	8,521	37,689	28,074
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	86,178	68,826	248,988	202,955
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	24,039	13,336	68,344	37,565
Intermodal [Member]
Operating revenue	31,903	26,747	100,512	74,343
Operating income:
Operating Income	778	2,840	9,911	6,151
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	24,303	22,716	77,589	64,193
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	7,600	4,031	22,923	10,150
Brokerage [Member]
Operating revenue	52,952	42,754	154,312	101,432
Operating income:
Operating Income	$ 5,664	$ 5,465	$ 16,983	$ 10,505