Note 6 - Segment Information - Segment Reporting Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Revenues from external customers	$ 1,930,707		$ 2,027,028		$ 3,781,537	$ 3,899,027
Cost of products sold	1,551,036		1,634,639		3,044,106	3,116,763
Controllable expenses	221,415		219,537		439,968	450,649
Allocated expenses	48,050		48,372		95,388	96,524
Segment operating income (loss)	110,206		124,481		202,075	235,091
Other Income	(372)		44		(812)	221
Interest income	365		342		1,039	543
Interest expense	13,091		19,806		26,629	37,980
Income taxes	24,119		26,278		42,068	47,603
Net income (loss)	72,989	$ 60,617	78,783	$ 71,489	133,606	150,272
Segment assets	4,715,774		4,506,526		4,715,774	4,506,526	$ 4,617,547
Capital expenditures	125,672		100,048		238,986	193,178
Depreciation and amortization	17,611		16,492		34,867	32,242
Operating Segments [Member] | Truck Segment [Member]
Revenues from external customers	1,926,222		2,022,756		3,773,566	3,890,803
Cost of products sold	1,550,455		1,634,108		3,043,162	3,115,761
Controllable expenses	219,008		217,818		436,216	447,433
Allocated expenses	47,110		46,277		92,428	92,269
Segment operating income (loss)	109,649		124,553		201,760	235,340
Other Income	(372)		44		(812)	221
Interest income	365		342		1,039	543
Interest expense	13,000		19,713		26,447	37,796
Income taxes	24,119		26,278		42,068	47,603
Net income (loss)	72,523		78,948		133,473	150,705
Segment assets	4,653,484		4,446,418		4,653,484	4,446,418
Capital expenditures	125,146		100,048		238,460	193,178
Depreciation and amortization	17,463		16,363		34,578	31,985
Operating Segments [Member] | Other Operating Segment [Member]
Revenues from external customers	4,485		4,272		7,971	8,224
Cost of products sold	581		531		945	1,002
Controllable expenses	2,407		1,719		3,751	3,217
Allocated expenses	941		2,095		2,962	4,254
Segment operating income (loss)	556		(73)		315	(249)
Other Income	0		0		0	0
Interest income	0		0		0	0
Interest expense	91		92		182	184
Income taxes	0		0		0	0
Net income (loss)	465		(165)		133	(433)
Segment assets	62,290		60,108		62,290	60,108
Capital expenditures	526		0		526	0
Depreciation and amortization	$ 148		$ 129		$ 288	$ 257