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, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 161,413		$ 156,964		$ 325,887		$ 308,438
Operating Income	13,121		13,283		25,659		22,802
Truckload Revenue, Net of Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating Revenue	99,996		94,148		194,961		183,346
Truckload Fuel Surcharge Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	26,856		26,121		53,625		51,374
Total Truckload Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	126,852		120,269		248,586		234,720
Logistics Revenue, Net of Intermodal Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating Revenue	29,721	[1]	33,045	[1]	67,481	[1]	66,481	[1]
Intermodal Fuel Surcharge Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	4,840		3,650		9,820		7,237
Total Logistics Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	34,561		36,695		77,301		73,718
Truckload [Member]
Segment Reporting Information [Line Items]
Operating Income	11,376		10,973		21,376		18,101
Logistics [Member]
Segment Reporting Information [Line Items]
Operating Income	$ 1,745		$ 2,310		$ 4,283		$ 4,701

[1] Logistics revenue is net of $2.1 million of inter-segment revenue in the six-month period ended June 30, 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. Inter-segment revenue was $2.4 million and $4.9 million for the three-month and six-month periods ended June 30, 2012.