Note 2 - Summary of Significant Accounting Policies - Change in Fair Value of Preferred Stock Warrant Liability (Details) - USD ($) $ in Thousands |
9 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2019 |
Sep. 30, 2018 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Derivative [Member] | ||||
| Change in value | $ (211) | |||
| Embedded derivative liability from the issuance of Notes | $ 864 | 864 | ||
| Termination of the embedded derivative liability due to the extinguishment of the related Notes | (211) | (653) | ||
| Fair value at end of period | 653 | |||
| Warrant [Member] | ||||
| Fair value, beginning of period | $ 140 | 42 | 42 | $ 54 |
| Preferred stock warrants - exercised | 94 | 1 | (8) | |
| Change in value | 98 | (4) | ||
| Exchange of warrants upon Merger | $ (234) | |||
| Fair value at end of period | $ 43 | $ 140 | $ 42 | |