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Note 2 - Investments | 12 Months Ended
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Dec. 31, 2017
Notes to Financial Statements |
Investments and Restricted Cash Disclosure [Text Block] | Note 2. Investments Investments Our current investments, which are classified as "available for sale" and consist of bonds having maturities of greater than 90 days and less than 365 days, had a fair value of $33.8 million and $29.1 million at December 31, 2017 and 2016, respectively. During 2017, we had purchases of such investments of $55.0 million and maturities of $50.0 million. Our current investments at December 31, 2017 and 2016 consisted of the following (in thousands):
|  | December 31, 2017 |  |  | December 31, 2016 |
|  | Amortized cost |  |  | Unrealized loss |  |  | Fair market value |  |  | Amortized cost |  |  | Unrealized loss |  |  | Fair market value |
Corporate bonds |  | $ | 33,778 |  |  | $ | (20 | ) |  | $ | 33,758 |  |  | $ | 22,100 |  |  | $ | (46 | ) |  | $ | 22,054 |
Municipal bonds |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 3,727 |  |  |  | (1 | ) |  |  | 3,726 |
Agency bonds |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 3,339 |  |  |  | (2 | ) |  |  | 3,337 |
Total |  | $ | 33,778 |  |  | $ | (20 | ) |  | $ | 33,758 |  |  | $ | 29,166 |  |  | $ | (49 | ) |  | $ | 29,117 |
At December 31, 2017 and 2016, the fair value of our non-current investments was $7.6 million and $5.0 million, respectively. Our non-current investments consist of marketable equity securities which are carried at fair value, and are primarily classified as “available-for-sale.” The cost basis of our non-current investments was approximately $5.7 million and $4.1 million at December 31, 2017 and 2016, respectively. In 2017 and 2016, we acquired marketable equity securities having a cost basis of $1.6 million and $0.9 million, respectively. In 2016, we recognized an impairment charge against current earnings of $1.0 million, as we determined the impairment to be other-than-temporary.

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