Note 4 - Related Party Transactions (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Payable, Related Parties	$ 0	$ 0
Purchase Of Fuel Tires And Related Services [Member]
Related Party Transaction, Amounts of Transaction	328,000	361,000	$ 335,000
Tire Purchases [Member]
Related Party Transaction, Amounts of Transaction	$ 2,500,000	$ 2,000,000	$ 1,500,000