Note 3 - Stockholders' Equity (Details Textual) - USD ($)		1 Months Ended			3 Months Ended	12 Months Ended
	Dec. 23, 2019	Aug. 31, 2019	Mar. 31, 2019	Feb. 28, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Common Stock and Preferred Stock, Shares Authorized						50,000,000
Common Stock and Preferred Stock, Par or Stated Value Per Share						$ 0.001
Common Stock, Shares Authorized						40,000,000	40,000,000
Preferred Stock, Shares Authorized						10,000,000	10,000,000
Proceeds from Issuance of Preferred Stock and Preference Stock							$ 25,106,896
Share Price			$ 11.50
Stock Issued During Period, Shares, New Issues			3,000,000		4,833,099
Proceeds from Issuance Initial Public Offering					$ 47,300,000	$ 63,039,490	$ 47,320,233
Convertible Preferred Stock, Shares Issued upon Conversion					9,948,207
Common Stock, Par or Stated Value Per Share						$ 0.001	$ 0.001
Proceeds from Issuance of Common Stock			$ 34,500,000
Proceeds from Issuance of Common Stock, Net of Offering Costs			$ 31,800,000
Warrants to Purchase Series D Preferred Stock [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				3,698,128
Warrants to Purchase Common Stock [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights					219,761
Class of Warrant or Right, Exercised During Period						64,629	48,836
Class of Warrant or Right, Outstanding						106,274
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 0.0168
ATM Agreement [Member]
Stock Issued During Period, Shares, New Issues						2,409,356
Proceeds from Issuance of Common Stock						$ 8,400,000
Proceeds from Issuance of Common Stock, Net of Offering Costs						$ 8,100,000
Private Placement [Member]
Stock Issued During Period, Shares, New Issues	7,164,534
Shares Issued, Price Per Share	$ 3.13
Proceeds from Issuance of Private Placement	$ 22,400,000
Proceeds from Issuance of Private Placement, Net of Offering Costs	$ 21,000,000
Jefferies, LLC [Member] | ATM Agreement [Member]
Sale of Stock, Maximum Aggregate Offering Price		$ 40,000,000
Sale of Stock, Commission Percentage		3.00%
Series D Preferred Stock [Member]
Proceeds from Issuance of Preferred Stock and Preference Stock				$ 25,600,000
Share Price				$ 0.59808
Stock Issued During Period, Value, Conversion of Convertible Securities				$ 28,900,000
Preferred Stock, Par or Stated Value Per Share						$ 0.001
Stock Issued During Period, Preferred Stock, Shares				91,147,482
Series C-1 Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share				$ 0.001
Nonvoting Common Stock, Class B [Member]
Common Stock, Par or Stated Value Per Share					$ 0.001