Note 13 - Business Segments (Detail) - Operating Revenue and Operating Income by Segment (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Operating Revenue	$ 166,412	$ 163,606	$ 156,964	$ 151,474	$ 158,340	$ 156,348	$ 151,135	$ 137,856	$ 638,456		$ 603,679		$ 516,920
Operating Income	13,211	9,840	13,283	9,519	12,951	11,111	11,359	7,609	45,853		43,030		35,289
Truckload Revenue, Net of Fuel Surcharge [Member]
Operating Revenue									378,383		357,787		325,791
Truckload Fuel Surcharge Revenue [Member]
Operating Revenue									104,940		98,060		66,973
Total Truckload Revenue [Member]
Operating Revenue									483,323		455,847		392,764
Logistics Revenue, Net of Intermodal Fuel Surcharge [Member]
Operating Revenue									138,960	[1]	132,890	[1]	115,223	[1]
Intermodal Fuel Surcharge Revenue [Member]
Operating Revenue									16,173		14,942		8,933
Total Logistics Revenue [Member]
Operating Revenue									155,133		147,832		124,156
Truckload [Member]
Operating Income									36,805		35,298		28,680
Logistics [Member]
Operating Income									$ 9,048		$ 7,732		$ 6,609

[1] Logistics revenue is net of $9.7 million, $9.0 million and $9.1 million of inter-segment revenue in 2012, 2011 and 2010, respectively, for loads transported by our tractors and arranged by MWL that have been eliminated in consolidation.