Note 8 - Warrants (Details Textual) - $ / shares
|
|
3 Months Ended |
|
|
|
May 14, 2020 |
Mar. 31, 2020 |
Dec. 31, 2019 |
May 31, 2016 |
Mar. 31, 2014 |
| Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) |
|
$ 4.33
|
$ 4.33
|
|
|
| Class of Warrant or Right, Exercised During Period (in shares) |
|
2,000
|
|
|
|
| Class of Warrant or Right, Outstanding (in shares) |
|
3,957,005
|
3,959,005
|
|
|
| Warrants to Purchase Common Stock [Member] |
|
|
|
|
|
| Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) |
|
|
|
|
6,910,283
|
| Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) |
|
|
|
|
$ 4.75
|
| Warrants in Connection with WAVI Credit Facility [Member] |
|
|
|
|
|
| Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) |
|
|
|
550,000
|
|
| Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) |
|
|
|
$ 1.75
|
|
| WAVI Holding AG and Taurus4757 GmbH Warrants [Member] | Subsequent Event [Member] |
|
|
|
|
|
| Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) |
$ 4.75
|
|
|
|
|
| Stock Issued During Period, Shares, Warrant Exercises (in shares) |
2,747,970
|
|
|
|
|
| Class of Warrant or Right, Exercised During Period (in shares) |
3,871,405
|
|
|
|
|
| Class of Warrant or Right, Outstanding (in shares) |
85,600
|
|
|
|
|