Note 7 - Segment Information - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenues from external customers	$ 1,348,317	$ 1,240,781
Segment operating income	56,867	32,389
Segment income (loss) before taxes	49,558	28,083
Segment assets	3,422,026	2,899,204	$ 3,201,350
Truck Segment [Member]
Revenues from external customers	1,344,449	1,236,652
Segment operating income	56,742	32,360
Segment income (loss) before taxes	49,505	28,103
Segment assets	3,384,441	2,864,504
Other Segments [Member]
Revenues from external customers	3,868	4,129
Segment operating income	125	29
Segment income (loss) before taxes	53	(20)
Segment assets	$ 37,585	$ 34,700