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Note 2 - Investments (Details Textual) - USD ($) $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017
Debt Securities, Available-for-sale, Current, Total | $ 34,358 |  | $ 33,758
Payments to Acquire Debt Securities, Available-for-sale | 31,200 | $ 11,100 |
Proceeds from Sale and Maturity of Marketable Securities, Total | 30,501 | 3,634 |
Equity Securities, FV-NI | 7,700 |  | 7,600
Equity Securities, FV-NI, Cost | 5,600 |  | 5,700
Equity Securities, Accumulated Unrealized Gain (Loss) | 2,100 |  | $ 1,900
Equity Securities, FV-NI, Unrealized Gain (Loss), Total | $ 300 | (300) |
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax |  | $ (300) |

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