Note 11 - Business Segments (Details) - Operating Revenue and Operating Income by Segment (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Segment Reporting Information [Line Items]
Operating Revenue	$ 168,423		$ 161,413		$ 327,832		$ 325,887
Operating Income	12,932		13,121		21,572		25,659
Truckload Revenue, Net of Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating Revenue	102,161		99,996		199,691		194,961
Truckload Fuel Surcharge Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	26,944		26,856		53,478		53,625
Total Truckload Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	129,105		126,852		253,169		248,586
Logistics Revenue, Net of Intermodal Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating Revenue	33,518	[1]	29,721	[1]	63,527	[1]	67,481	[1]
Intermodal Fuel Surcharge Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	5,800		4,840		11,136		9,820
Total Logistics Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	39,318		34,561		74,663		77,301
Truckload [Member]
Segment Reporting Information [Line Items]
Operating Income	11,843		11,376		19,343		21,376
Logistics [Member]
Segment Reporting Information [Line Items]
Operating Income	$ 1,089		$ 1,745		$ 2,229		$ 4,283

[1] Logistics revenue is net of $2.1 million of inter-segment revenue in the three-month period ended March 31, 2013 for loads transported by our tractors and arranged by MWL prior to the deconsolidation of MWL effective March 28, 2013. Such revenue has been eliminated in consolidation.