Note 7 - Stockholders' Equity and Common Stock Warrants - Warrants Outstanding to Acquire Shares of Its Common Stock (Details)	Jun. 30, 2022 $ / shares shares
Common stock warrants, outstanding (in shares) | shares	111,891
Warrants Issued in Connection with the January 2018 Offering [Member]
Common stock warrants, outstanding (in shares) | shares	23,639
Warrants Issued in Connection with the January 2018 Offering [Member] | Minimum [Member]
Range of exercise price (in dollars per share)	$ 599.71
Warrants Issued in Connection with the January 2018 Offering [Member] | Maximum [Member]
Range of exercise price (in dollars per share)	$ 749.76
Warrants Issued in Connection with May 2019 Public Offering [Member]
Common stock warrants, outstanding (in shares) | shares	27,648
Warrants Issued in Connection with May 2019 Public Offering [Member] | Minimum [Member]
Range of exercise price (in dollars per share)	$ 250.09
Warrants Issued in Connection with May 2019 Public Offering [Member] | Maximum [Member]
Range of exercise price (in dollars per share)	$ 306.04
Warrants Issued in Connection with the November 2019 Offering [Member]
Common stock warrants, outstanding (in shares) | shares	4,269
Range of exercise price (in dollars per share)	$ 17.51
Warrants Issued in Connection with the December 2019 Offering [Member]
Common stock warrants, outstanding (in shares) | shares	6,264
Warrants Issued in Connection with the December 2019 Offering [Member] | Minimum [Member]
Range of exercise price (in dollars per share)	$ 21.68
Warrants Issued in Connection with the December 2019 Offering [Member] | Maximum [Member]
Range of exercise price (in dollars per share)	$ 34.92
Common Stock Warrants Issued Related to May 2020 Common Stock Offering [Member]
Common stock warrants, outstanding (in shares) | shares	11,424
Range of exercise price (in dollars per share)	$ 65.65
The May 2020 Investor Warrant Exercise [Member]
Common stock warrants, outstanding (in shares) | shares	4,998
Range of exercise price (in dollars per share)	$ 29.7
Common Stock Warrants Issued Related to February 2021 Common Stock Offering [Member]
Common stock warrants, outstanding (in shares) | shares	33,649
Range of exercise price (in dollars per share)	$ 64.08