Note 5 - Revenues - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for doubtful accounts, Balance	$ 267	$ 263	$ 255	$ 237
Provision for losses on accounts receivable	9	11	27	34
Write-offs	(3)		(9)
Allowance for doubtful accounts, Balance	$ 273	268	$ 273	268
Recoveries		$ (6)		$ (3)