Note 7 - Segment Information (Details) - Segment Reporting Information (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues from external customers	$ 913,064	$ 745,133	$ 2,459,526	$ 2,358,306
Segment income (loss) before taxes	25,089	24,244	56,498	78,879
Segment assets	2,045,530	1,862,928	2,045,530	1,862,928	1,881,566
Truck Segment [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	907,903	740,392	2,445,151	2,344,073
Segment income (loss) before taxes	25,149	24,704	56,685	79,521
Segment assets	2,016,725	1,835,675	2,016,725	1,835,675
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	5,161	4,741	14,375	14,233
Segment income (loss) before taxes	(60)	(460)	(187)	(642)
Segment assets	$ 28,806	$ 27,253	$ 28,806	$ 27,253