Note 3 - Segment Information - Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues	$ 178,631	$ 164,500	$ 501,701	$ 479,673
Operating income (loss)	9,041	5,446	13,312	20,181
Operating Segments [Member] | Truckload [Member]
Revenues	153,066	148,603	446,322	436,055
Operating income (loss)	11,165	5,508	20,054	22,558
Operating Segments [Member] | Other Segments [Member]
Revenues	25,565	15,897	55,379	43,618
Operating income (loss)	2,468	1,829	5,500	5,144
Corporate, Non-Segment [Member]
Operating income (loss)	$ (4,592)	$ (1,891)	$ (12,242)	$ (7,521)