Note 7 - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Truck Segment [Member]
Revenues from external customers	$ 1,022,547	$ 1,326,360	$ 2,089,837	$ 2,516,347
Segment income (loss) before taxes	17,865	32,159	22,235	59,911
Segment assets	2,779,789	2,715,032	2,779,789	2,715,032
Other Segments [Member]
Revenues from external customers	3,915	3,943	7,465	7,491
Segment income (loss) before taxes	(56)	(197)	(484)	(561)
Segment assets	32,906	31,984	32,906	31,984
Revenues from external customers	1,026,462	1,330,303	2,097,302	2,523,838
Segment income (loss) before taxes	17,809	31,962	21,751	59,350
Segment assets	$ 2,812,695	$ 2,747,016	$ 2,812,695	$ 2,747,016	$ 2,852,008