Note 6 - Valuation Accounts - Valuation and Allowance Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Parts Inventory [Member]
Balance	$ 7,661	$ 7,050	$ 6,230
Net Charged to Costs and Expenses	4,501	4,460	2,744
Net Write-Offs	(2,847)	(3,849)	(1,924)
Balance End of Year	9,315	7,661	7,050
Commercial Vehicle Inventory [Member]
Balance	9,602	4,587	5,953
Net Charged to Costs and Expenses	9,598	12,489	3,550
Net Write-Offs	(13,125)	(7,474)	(4,916)
Balance End of Year	6,075	9,602	4,587
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
Balance	1,014	987	616
Net Charged to Costs and Expenses		2,065	2,183
Net Write-Offs		(2,038)	(1,812)
Balance End of Year		1,014	987
Allowance for Warranty Receivables From Manufacturers [Member]
Balance	$ 410	429	210
Net Charged to Costs and Expenses		1,661	2,031
Net Write-Offs		(1,680)	(1,812)
Balance End of Year		$ 410	$ 429