Note 11 - Stockholders' Equity - Summary of Warrant Activity (Details) - $ / shares
|
12 Months Ended |
Dec. 31, 2021 |
Dec. 31, 2020 |
| Stock purchase warrants exercised, number (in shares) |
(1,815,012,000)
|
(5,155,976)
|
| Purchase Warrants [Member] |
|
|
| Stock purchase warrants outstanding, number (in shares) |
3,206,910
|
6,620,620
|
| Shares purchasable under outstanding warrants, exercise price (in dollars per share) |
$ 6.36
|
$ 5.41
|
| Stock purchase warrants issued, number (in shares) |
|
2,066,667
|
| Stock purchase warrants issued, exercise price (in dollars per share) |
|
$ 6.00
|
| Stock purchase warrants exercised, number (in shares) |
(1,815,012)
|
(5,155,976)
|
| Stock purchase warrants exercised, exercise price (in dollars per share) |
$ 6.64
|
$ 5.08
|
| Stock purchase warrants expired (in shares) |
(231)
|
(324,401)
|
| Stock purchase warrants expired (in dollars per share) |
$ 7.58
|
$ 5.00
|
| Stock purchase warrants outstanding, number (in shares) |
1,391,667
|
3,206,910
|
| Shares purchasable under outstanding warrants, exercise price (in dollars per share) |
$ 6.00
|
$ 6.36
|