Note 6 - Stockholders' Equity (Details Textual) - USD ($)					1 Months Ended		9 Months Ended	12 Months Ended
	Nov. 10, 2020	May 15, 2020	Feb. 20, 2019	Aug. 09, 2017	Nov. 30, 2020	Mar. 31, 2019	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2017
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)										2,646,091
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)										$ 7.50
Warrants and Rights Outstanding, Term (Year)										10 years
Proceeds from Issuance of Common Stock, Net Issuance Costs								$ 16,819,627	$ 2,103,788
Preferred Stock, Par or Stated Value Per Share (in dollars per share)								$ 0.001	$ 0.001
Dividends, Common Stock, Total								$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)								1,511,000	714,350
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount								$ 4,800,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)								2 years 182 days
Share-based Payment Arrangement, Expense								$ 1,300,000	$ 900,000
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expense								1,270,000	900,000
Research and Development Expense [Member]
Share-based Payment Arrangement, Expense								$ 20,000	$ 3,607,000,000
The 2018 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)	1,750,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	3,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)	957,650
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)								1,511,000	714,350
Share-based Compensation Arrangement by Share-based Payment Award, Options, Granted in Period, Fair Value								$ 4,300,000	$ 2,900,000
The 2018 Incentive Plan [Member] | Employees [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)								6 years	6 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate									82.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate								0.00%	0.00%
The 2018 Incentive Plan [Member] | Employees [Member] | Share-based Payment Arrangement, Option [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Discount Rate								0.40%	1.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate								81.00%
The 2018 Incentive Plan [Member] | Employees [Member] | Share-based Payment Arrangement, Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Discount Rate								0.70%	2.50%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate								84.00%
Warrants Issued in Connection with Term Loan Facility [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				58,502
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 6.41
Class of Warrant or Right, Term (Year)				10 years
Series A Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)			15,000
Proceeds from Issuance of Private Placement			$ 15,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)			$ 0.001
Shares Issued, Price Per Share (in dollars per share)			1,000
Preferred Stock, Convertible, Conversion Price (in dollars per share)			$ 2.60
Preferred Stock, Dividend Rate, Percentage			8.00%
Preferred Stock, Liquidation Preference, Value			$ 1,000
Adjustments to Additional Paid in Capital, Preferred Stock Beneficial Conversion Feature at Issuance									$ 12,700,000
Adjustments to Additional Paid in Capital, Preferred Stock Beneficial Conversion Feature, Deemed Dividend									12,700,000
Temporary Equity, Par Value								$ 13,700,000
Payments of Stock Issuance Costs								1,300,000
Dividends, Preferred Stock, Total								$ 1,300,000	$ 1,100,000
Preferred Stock, Dividends Per Share, Declared (in dollars per share)								$ 0.14	$ 0.12
Series B Preferred Stock [Member]
Shares Issued, Price Per Share (in dollars per share)		$ 1,000
Preferred Stock, Convertible, Conversion Price (in dollars per share)		$ 3.10
Preferred Stock, Dividend Rate, Percentage		8.00%
Preferred Stock, Liquidation Preference, Value		$ 1,000
Temporary Equity, Par Value								$ 7,700,000
Payments of Stock Issuance Costs								300,000
Dividends, Preferred Stock, Total								$ 0.40
Preferred Stock, Dividends Per Share, Declared (in dollars per share)								$ 0.04
JMP Securities, Inc [Member]
Stock Issued During Period, Shares, New Issues (in shares)							0		398,709
Distribution Agreement, Aggregate Sales Price						$ 12,500,000
Public Offering Price Allowed under Shelf Registration, Total						$ 75,000,000
Proceeds from Issuance of Common Stock									$ 2,300,000
Proceeds from Issuance of Common Stock, Net Issuance Costs									$ 2,100,000
Distribution Agreement, Amount Available for Sale								$ 10,200,000
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)								4,755,373	398,709
Private Placement [Member]
Proceeds from Issuance or Sale of Equity, Total					$ 18,000,000
Proceeds from Issuance or Sale of Equity, Net of Allocated Issuance Costs					$ 16,800,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)					5,230,910
Stock Issued Per Unit Price (in dollars per share)					$ 3.787
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)					$ 4.31
Warrants and Rights Outstanding, Term (Year)					5 years
Private Placement [Member] | Series B Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)		8,000
Proceeds from Issuance of Private Placement		$ 8,000,000
Private Placement [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)					4,755,373