Note 10 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| Stock-based compensation expense | $ 1,346 | $ 1,048 | $ 2,453 | $ 2,128 |
| Cost of Sales [Member] | ||||
| Stock-based compensation expense | 68 | 74 | 129 | 161 |
| Research and Development Expense [Member] | ||||
| Stock-based compensation expense | 233 | 377 | 457 | 809 |
| Selling, General and Administrative Expenses [Member] | ||||
| Stock-based compensation expense | $ 1,045 | $ 597 | $ 1,867 | $ 1,158 |