Note 6 - Valuation Accounts - Valuation and Allowance Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
Balance	$ 987	$ 616	$ 549
Net Charged to Costs and Expenses	2,065	2,183	625
Net Write-Offs	(2,038)	(1,812)	(558)
Balance End of Year	1,014	987	616
Allowance for Warranty Receivables From Manufacturers [Member]
Balance	429	210	114
Net Charged to Costs and Expenses	1,661	2,031	713
Net Write-Offs	(1,680)	(1,812)	(617)
Balance End of Year	410	429	210
Parts Inventory [Member]
Balance	7,050	6,230	4,885
Net Charged to Costs and Expenses	4,460	2,744	1,414
Net Write-Offs	(3,849)	(1,924)	(69)
Balance End of Year	7,661	7,050	6,230
Commercial Vehicle Inventory [Member]
Balance	4,587	5,953	5,102
Net Charged to Costs and Expenses	12,489	3,550	5,997
Net Write-Offs	(7,474)	(4,916)	(5,146)
Balance End of Year	$ 9,602	$ 4,587	$ 5,953