Note 7 - Financial Instruments and Investments in Securities - Contractual Maturity (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Due in one year or less, amortized cost	$ 499,528
Due in one year or less, estimated fair value	500,211
Due after one year through five years, amortized cost
Due after one year through five years, estimated fair value
Total, amortized cost	499,528
Held-to-maturity securities, fair value, total	$ 500,211

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

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