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Note 6 - Trade Receivables (Details Textual) - USD ($)
Mar. 31, 2021
Dec. 31, 2020
Mar. 31, 2020
Accounts Receivable, Allowance for Credit Loss, Current $ 394,000 $ 242,000 $ 262,000
Contract with Customer, Refund Liability, Current $ 1,619,000 $ 1,348,000 $ 838,000