Note 6 - Marketable Securities - Balance of Held-to-maturity Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Due in one year or less	$ 35,045
Due after one year through five years	18,262
Total marketable securities	$ 53,307	$ 70,329

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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