Note 2 - Allowance for Doubtful Accounts Receivable - Allowance for Doubtful Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance at the beginning of year	$ 1,382	$ 1,276	$ 848
Provision for bad debts - accounts receivable	867	1,002	512
Charge-offs	(210)	(901)	(96)
Recoveries	3	5	1
Balance at the end of year	$ 2,042	$ 1,382	$ 1,276