Note 6 - Stockholders' Equity	9 Months Ended
Sep. 30, 2020
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	Note 6 - Stockholders’ Equity On April 24, 2020, the Company filed a $500,000 shelf registration statement on Form S-3 with the SEC. This shelf registration statement became effective on May 14, 2020 and allows the Company to sell securities, including common stock, preferred stock, depository shares, purchase contracts, warrants, debt securities and units, from time to time at prices and on terms to be determined at the time of sale. On June 1, 2020, the Company completed an underwritten public offering of 22,044,447 shares of its common stock (including shares issued pursuant to the underwriters’ 30-day option to purchase additional shares, which was exercised in full), at a purchase price of $4.50 per share, and pre-funded warrants to purchase 3,511,111 shares of common stock, at a purchase price of $4.49 per pre-funded warrant, for total net proceeds to the Company of $107,665 after deducting underwriting discounts and commissions and other offering expenses payable by the Company. The pre-funded warrants are exercisable, subject to the conditions in the warrant agreement, and have an exercise price of $0.01 per share, which is subject to adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications, or similar events affecting the Company’s common stock and also upon any distributions of assets to the Company’s stockholders.

Note 6 - Stockholders' Equity

9 Months Ended

Sep. 30, 2020

Stockholders' Equity Note Disclosure [Text Block]

Note 6 - Stockholders’ Equity

On April 24, 2020, the Company filed a $500,000 shelf registration statement on Form S-3 with the SEC. This shelf registration statement became effective on May 14, 2020 and allows the Company to sell securities, including common stock, preferred stock, depository shares, purchase contracts, warrants, debt securities and units, from time to time at prices and on terms to be determined at the time of sale. On June 1, 2020, the Company completed an underwritten public offering of 22,044,447 shares of its common stock (including shares issued pursuant to the underwriters’ 30-day option to purchase additional shares, which was exercised in full), at a purchase price of $4.50 per share, and pre-funded warrants to purchase 3,511,111 shares of common stock, at a purchase price of $4.49 per pre-funded warrant, for total net proceeds to the Company of $107,665 after deducting underwriting discounts and commissions and other offering expenses payable by the Company. The pre-funded warrants are exercisable, subject to the conditions in the warrant agreement, and have an exercise price of $0.01 per share, which is subject to adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications, or similar events affecting the Company’s common stock and also upon any distributions of assets to the Company’s stockholders.