Note F - Segment Information - Segment Revenue Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Revenue, before fuel surcharges	$ 129,155	$ 128,686
Freight Transportation Service [Member]
Revenue, before fuel surcharges	$ 111,822	$ 110,345
Freight Transportation Service [Member] \| Revenue Benchmark [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	$ 91,311	$ 90,013
Truckload Services [Member] \| Freight Transportation Service [Member] \| Revenue Benchmark [Member] \| Product Concentration Risk [Member]
Revenue, before fuel surcharges, percentage	81.70%	81.60%
Brokerage and Logistics Services [Member] \| Freight Transportation Service [Member]
Revenue, before fuel surcharges	$ 20,511	$ 20,332
Brokerage and Logistics Services [Member] \| Freight Transportation Service [Member] \| Revenue Benchmark [Member] \| Product Concentration Risk [Member]
Revenue, before fuel surcharges, percentage	18.30%	18.40%

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 924
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-Section S99
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+ Details