Note 6 - Trade Receivables (Details Textual) - USD ($)	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Accounts Receivable, Allowance for Credit Loss, Current	$ 1,062,000	$ 242,000	$ 278,000
Contract with Customer, Refund Liability, Current	$ 2,057,000	$ 1,348,000	$ 805,000