Note 6 - Valuation Accounts - Valuation and Allowance Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Trade Receivables [Member]
Balance	$ 506	$ 639	$ 821
Net Charged to Costs and Expenses	1,415	992	919
Net Write-Offs	(1,372)	(1,125)	(1,101)
Balance End of Year	549	506	639
Allowance for Warranty Receivables From Manufacturers [Member]
Balance	105	140	419
Net Charged to Costs and Expenses	833	1,677	411
Net Write-Offs	(824)	(1,712)	(690)
Balance End of Year	114	105	140
Parts Inventory [Member]
Balance	7,291	5,067	4,416
Net Charged to Costs and Expenses	3,400	4,215	2,547
Net Write-Offs	(5,806)	(1,991)	(1,896)
Balance End of Year	4,885	7,291	5,067
Commercial Vehicle Inventory [Member]
Balance	6,541	10,644	7,395
Net Charged to Costs and Expenses	9,623	8,417	7,877
Net Write-Offs	(11,062)	(12,520)	(4,628)
Balance End of Year	$ 5,102	$ 6,541	$ 10,644