Note 9 - Details of Selected Balance Sheet Accounts - Summary of Accounts Receivable (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Accounts receivable, principally trade		$ 11,186	$ 10,458
Less: allowance for expected credit losses	[1]	(2,729)	(2,413)
Accounts receivable, net		$ 8,457	$ 8,045

[1] Allowance for expected credit losses primarily relates to two customers with outstanding receivable balance determined to be uncollectible in the fourth quarter of 2020.