Note 2 - Allowance for Doubtful Accounts Receivable - Allowance for Doubtful Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance at the beginning of year	$ 1,276	$ 848	$ 680
Provision for bad debts - accounts receivable	1,002	512	266
Charge-offs	(901)	(96)	(98)
Recoveries	5	1
Balance at the end of year	$ 1,382	$ 1,276	$ 848