Note 7 - Segment Information - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Truck Segment [Member]
Revenues from external customers	$ 1,092,005	$ 1,289,929	$ 3,181,842	$ 3,806,276
Segment income (loss) before taxes	24,505	33,069	46,740	92,981
Segment assets	2,662,872	2,837,256	2,662,872	2,837,256
Other Segments [Member]
Revenues from external customers	4,036	4,147	11,501	11,638
Segment income (loss) before taxes	(202)	(607)	(686)	(1,169)
Segment assets	32,623	33,234	32,623	33,234
Revenues from external customers	1,096,041	1,294,076	3,193,343	3,817,914
Segment income (loss) before taxes	24,303	32,462	46,054	91,812
Segment assets	$ 2,695,495	$ 2,870,490	$ 2,695,495	$ 2,870,490	$ 2,852,008