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Note 5 - Marketable Securities - Summary of Gross Unrealized Losses and Fair Values on Investments (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Less than 12 months, Fair value $ 32,679 $ 31,393
Less than 12 months, Gross unrealized loss (382) (91)
12 months or greater, Fair value 8,372 7,381
12 months or greater, Gross unrealized loss $ (29) $ (21)