Note 2 - Allowance for Doubtful Accounts Receivable - Allowance for Doubtful Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance at the beginning of year	$ 2,042	$ 1,382	$ 1,276
Provision for bad debts - accounts receivable	1,323	867	1,002
Charge-offs	(401)	(210)	(901)
Recoveries		3	5
Balance at the end of year	$ 2,964	$ 2,042	$ 1,382