Note 2 - Investments and Fair Value Measurement - Summary of Changes in Fair Value of Level III Financial Liabilities (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| Fair value, Beginning of period | $ 98 | $ 186 | $ 121 | $ 207 |
| Fair value of contingent put option associated with the Loan Agreement | 657 | 657 | ||
| Change in fair value of contingent put option associated with the Prior Agreement | (98) | (20) | (121) | (41) |
| Fair value, End of period | $ 657 | $ 166 | $ 657 | $ 166 |