Note 17 - Segments - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from external customers	$ 1,268,197	$ 1,178,568	$ 1,002,512	$ 1,286,663	$ 1,317,704	$ 1,599,265	$ 1,544,561	$ 1,348,317	$ 4,735,940	$ 5,809,847	$ 5,506,190
Interest income									713	1,680	1,376
Interest expense									9,727	30,487	21,058
Depreciation and amortization									57,456	55,372	70,489
Segment operating income	53,539	42,868	23,001	35,197	39,423	58,323	61,792	56,867	154,605	216,405	202,851
Segment income from continuing operations before taxes	53,614	$ 43,928	$ 22,512	$ 31,669	33,345	$ 52,210	$ 54,410	$ 49,558	151,723	189,523	183,169
Segment assets	2,985,393				3,407,329				2,985,393	3,407,329	3,201,350
Goodwill	292,142				292,142				292,142	292,142	291,391
Expenditures for segment assets									136,200	293,493	238,260
Truck Segment [Member]
Revenues from external customers									4,721,058	5,794,155	5,488,787
Interest income									713	1,680	1,376
Interest expense									9,444	30,201	20,850
Depreciation and amortization									57,162	55,036	70,170
Segment operating income									153,841	216,691	202,725
Segment income from continuing operations before taxes									151,222	188,122	183,251
Segment assets	2,939,390				3,369,517				2,939,390	3,369,517	3,166,174
Goodwill	289,582				289,582				289,582	289,582	288,831
Expenditures for segment assets									135,956	292,980	238,229
Other Segments [Member]
Revenues from external customers									14,882	15,692	17,403
Interest income									0	0	0
Interest expense									283	286	208
Depreciation and amortization									294	336	319
Segment operating income									764	(286)	126
Segment income from continuing operations before taxes									501	1,401	(82)
Segment assets	46,003				37,812				46,003	37,812	35,176
Goodwill	$ 2,560				$ 2,560				2,560	2,560	2,560
Expenditures for segment assets									$ 244	$ 513	$ 31