Note 6 - Revenues - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Allowance for doubtful accounts, Balance	$ 260	$ 277	$ 265	$ 275
Provision for losses on accounts receivable	6	9	0	14
Write-offs less recoveries	(16)	(15)	(15)	(18)
Allowance for doubtful accounts, Balance	$ 250	$ 271	$ 250	$ 271