Note 6 - Valuation Accounts - Valuation and Allowance Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
Balance	$ 616	$ 549	$ 506
Net Charged to Costs and Expenses	2,183	625	1,415
Net Write-Offs	(1,812)	(558)	(1,372)
Balance End of Year	987	616	549
Allowance for Warranty Receivables From Manufacturers [Member]
Balance	210	114	105
Net Charged to Costs and Expenses	2,031	713	833
Net Write-Offs	(1,812)	(617)	(824)
Balance End of Year	429	210	114
Parts Inventory [Member]
Balance	6,230	4,885	7,291
Net Charged to Costs and Expenses	2,744	1,414	3,400
Net Write-Offs	(1,924)	(69)	(5,806)
Balance End of Year	7,050	6,230	4,885
Commercial Vehicle Inventory [Member]
Balance	5,953	5,102	6,541
Net Charged to Costs and Expenses	3,550	5,997	9,623
Net Write-Offs	(4,916)	(5,146)	(11,062)
Balance End of Year	$ 4,587	$ 5,953	$ 5,102