Note 7 - Segment Information - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenues from external customers	$ 1,178,568	$ 1,599,265	$ 3,467,743	$ 4,492,143
Segment operating income	42,868	58,323	101,066	176,982
Segment income before taxes	43,928	52,210	98,109	156,178
Segment assets	3,010,689	3,405,254	3,010,689	3,405,254	$ 3,407,329
Truck Segment [Member]
Revenues from external customers	1,174,662	1,595,285	3,456,780	4,479,972
Segment operating income	42,714	58,642	100,842	176,963
Segment income before taxes	43,844	51,250	98,097	155,024
Segment assets	2,965,188	3,364,895	2,965,188	3,364,895
Other Segments [Member]
Revenues from external customers	3,906	3,980	10,963	12,171
Segment operating income	154	(319)	224	19
Segment income before taxes	84	960	12	1,154
Segment assets	$ 45,501	$ 40,359	$ 45,501	$ 40,359