Note 11 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Operating revenue	$ 329,565	$ 232,442	$ 616,846	$ 455,488
Operating income:
Operating Income	40,937	28,518	76,795	52,516
Truckload [Member]
Operating revenue	126,972	95,941	239,762	190,856
Operating income:
Operating Income	16,088	13,197	31,659	24,612
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	101,808	83,633	196,978	167,552
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	25,164	12,308	42,784	23,304
Dedicated [Member]
Operating revenue	110,355	80,121	207,115	158,358
Operating income:
Operating Income	14,039	10,617	24,684	19,553
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	84,389	67,227	162,810	134,129
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	25,966	12,894	44,305	24,229
Intermodal [Member]
Operating revenue	36,967	25,592	68,609	47,596
Operating income:
Operating Income	4,097	1,850	9,133	3,311
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	27,681	22,031	53,286	41,477
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	9,286	3,561	15,323	6,119
Brokerage [Member]
Operating revenue	55,271	30,788	101,360	58,678
Operating income:
Operating Income	$ 6,713	$ 2,854	$ 11,319	$ 5,040