Note F - Segment Information - Segment Revenue Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, before fuel surcharges	$ 119,458	$ 109,405
Freight Transportation Service [Member]
Revenue, before fuel surcharges	$ 99,104	$ 93,603
Freight Transportation Service [Member] | Sales Revenue, Net [Member] | Product Concentration Risk [Member]
Revenue, before fuel surcharges, percentage	100.00%	100.00%
Truckload Services [Member] | Freight Transportation Service [Member]
Revenue, before fuel surcharges	$ 80,524	$ 82,918
Truckload Services [Member] | Freight Transportation Service [Member] | Sales Revenue, Net [Member] | Product Concentration Risk [Member]
Revenue, before fuel surcharges, percentage	81.30%	88.60%
Brokerage and Logistics Services [Member] | Freight Transportation Service [Member]
Revenue, before fuel surcharges	$ 18,580	$ 10,685
Brokerage and Logistics Services [Member] | Freight Transportation Service [Member] | Sales Revenue, Net [Member] | Product Concentration Risk [Member]
Revenue, before fuel surcharges, percentage	18.70%	11.40%