Note 11 - Business Segments (Details) - Operating Revenue and Operating Income by Segment (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]
Operating Revenue	$ 171,550		$ 167,103		$ 499,382		$ 492,990
Operating Income	13,042		13,653		34,614		39,312
Truckload Revenue, Net of Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating Revenue	105,271		103,145		304,962		298,106
Truckload Fuel Surcharge Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	25,816		27,135		79,294		80,760
Total Truckload Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	131,087		130,280		384,256		378,866
Logistics Revenue, Net of Intermodal Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating Revenue	34,670	[1]	31,397	[1]	98,197	[1]	98,878	[1]
Intermodal Fuel Surcharge Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	5,793		5,426		16,929		15,246
Total Logistics Revenue [Member]
Segment Reporting Information [Line Items]
Operating Revenue	40,463		36,823		115,126		114,124
Truckload [Member]
Segment Reporting Information [Line Items]
Operating Income	12,501		12,267		31,844		33,643
Logistics [Member]
Segment Reporting Information [Line Items]
Operating Income	$ 541		$ 1,386		$ 2,770		$ 5,669

[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.