Note 13 - Subsequent Events	6 Months Ended
Jun. 30, 2021
Notes to Financial Statements
Subsequent Events [Text Block]	13. Subsequent Events In July 2021, we entered into a Side Letter (the “Side Letter”) with B. Riley Securities, Inc. (the “Agent”) in connection with the At-Market Issuance Sales Agreement dated April 2, 2021 (the “Sales Agreement”) between us and the Agent. The Side Letter confirmed the understanding of the parties that the Sales Agreement applies to the issuance and sale of shares (the “Shares”) of our common stock having an aggregate offering price of up to $50.0 million pursuant to our existing shelf registration statement on Form S-3 (File No. 333-254458) originally filed with the SEC on March 18, 2021 and which became effective on March 26, 2021 (the “Registration Statement”). All other terms and conditions of the Sales Agreement remain in full force and effect. We previously filed a prospectus supplement dated April 2, 2021 relating to the offering of up to $25.0 million in Shares under the Sales Agreement (the “Prior Offering”). We also filed a prospectus supplement dated July 7, 2021 relating to the offering of up to an additional $25.0 million in Shares under the Sales Agreement (the “Current Offering”). During July 2021, we received $31.8 million in net cash proceeds from the sale of 6,793,798 Shares, no par value under the terms of the Prior Offering and the Current Offering.

Note 13 - Subsequent Events

6 Months Ended

Jun. 30, 2021

13. Subsequent Events

In July 2021, we entered into a Side Letter (the “Side Letter”) with B. Riley Securities, Inc. (the “Agent”) in connection with the At-Market Issuance Sales Agreement dated April 2, 2021 (the “Sales Agreement”) between us and the Agent. The Side Letter confirmed the understanding of the parties that the Sales Agreement applies to the issuance and sale of shares (the “Shares”) of our common stock having an aggregate offering price of up to $50.0 million pursuant to our existing shelf registration statement on Form S-3 (File No. 333-254458) originally filed with the SEC on March 18, 2021 and which became effective on March 26, 2021 (the “Registration Statement”). All other terms and conditions of the Sales Agreement remain in full force and effect.

We previously filed a prospectus supplement dated April 2, 2021 relating to the offering of up to $25.0 million in Shares under the Sales Agreement (the “Prior Offering”). We also filed a prospectus supplement dated July 7, 2021 relating to the offering of up to an additional $25.0 million in Shares under the Sales Agreement (the “Current Offering”).

During July 2021, we received $31.8 million in net cash proceeds from the sale of 6,793,798 Shares, no par value under the terms of the Prior Offering and the Current Offering.