Note 11 - Revenue and Business Segments - Operating Revenue and Operating Income by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating revenue	$ 287,281	$ 223,046
Operating Income	35,858	23,998
Truckload [Member]
Operating revenue	112,790	94,915
Operating Income	15,571	11,415
Truckload [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	95,170	83,919
Truckload [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	17,620	10,996
Dedicated [Member]
Operating revenue	96,760	78,237
Operating Income	10,645	8,936
Dedicated [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	78,421	66,902
Dedicated [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	18,339	11,335
Intermodal [Member]
Operating revenue	31,642	22,004
Operating Income	5,036	1,461
Intermodal [Member] | Revenue, Net of Fuel Surcharge [Member]
Operating revenue	25,605	19,446
Intermodal [Member] | Fuel Surcharge Revenue [Member]
Operating revenue	6,037	2,558
Brokerage [Member]
Operating revenue	46,089	27,890
Operating Income	$ 4,606	$ 2,186