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, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Operating revenue	$ 285,672	$ 329,565	$ 583,695	$ 616,846
Operating income	28,213	40,937	57,223	76,795
Truckload [Member]
Operating revenue	117,138	126,972	237,764	239,762
Operating income	9,569	16,088	19,610	31,659
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	101,268	101,808	203,588	196,978
Truckload [Member] | Truckload Fuel Surcharge Revenue [Member]
Operating revenue	15,870	25,164	34,176	42,784
Dedicated [Member]
Operating revenue	104,985	110,355	211,434	207,115
Operating income	14,173	14,039	27,857	24,684
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	87,437	84,389	174,268	162,810
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	17,548	25,966	37,166	44,305
Intermodal [Member]
Operating revenue	22,365	36,967	50,954	68,609
Operating income	(165)	4,097	622	9,133
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	18,754	27,681	42,155	53,286
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	3,611	9,286	8,799	15,323
Brokerage [Member]
Operating revenue	41,184	55,271	83,543	101,360
Operating income	$ 4,636	$ 6,713	$ 9,134	$ 11,319