Note 16 - Subsequent Events (Details Textual) - $ / shares | Mar. 10, 2020 | Dec. 31, 2019 | Dec. 31, 2018 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | 2,160,000 | 2,320,000 |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | | $ 2 | $ 2.98 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | | 312,000 | 114,000 |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price | | $ 2.32 | $ 2.04 |
Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | 160,000 | 166,000 |
Employee Stock Option Vesting Schedule II [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | 335,000 | 850,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 100.00% | |
Share-based Payment Arrangement, Tranche One [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 50.00% | |
Share-based Payment Arrangement, Tranche One [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 50.00% | 50.00% |
Share-based Payment Arrangement, Tranche Two [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 16.67% | 16.67% |
Share-based Payment Arrangement, Tranche Two [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 25.00% | 25.00% |
Share-based Payment Arrangement, Tranche Three [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 16.67% | 16.67% |
Share-based Payment Arrangement, Tranche Three [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 25.00% | 25.00% |
Share-based Compensation Award, Tranche Four [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | 16.67% | 16.67% |
Subsequent Event [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | 5,808,834 | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price | $ 6.82 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | 161,775 | | |
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price | $ 2.68 | | |
Subsequent Event [Member] | Employee Stock Option Vesting Schedule II [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | 861,834 | | |
Subsequent Event [Member] | Share-based Payment Arrangement, Tranche One [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 50.00% | | |
Subsequent Event [Member] | Share-based Payment Arrangement, Tranche One [Member] | Employee Stock Option Vesting Schedule II [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 50.00% | | |
Subsequent Event [Member] | Share-based Payment Arrangement, Tranche Two [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 16.67% | | |
Subsequent Event [Member] | Share-based Payment Arrangement, Tranche Two [Member] | Employee Stock Option Vesting Schedule II [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 25.00% | | |
Subsequent Event [Member] | Share-based Payment Arrangement, Tranche Three [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 16.67% | | |
Subsequent Event [Member] | Share-based Payment Arrangement, Tranche Three [Member] | Employee Stock Option Vesting Schedule II [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 25.00% | | |
Subsequent Event [Member] | Share-based Compensation Award, Tranche Four [Member] | Employee Stock Option Vesting Schedule I [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | 16.67% | | |