Note 1 - Organization and Basis of Presentation (Details Textual)					3 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Apr. 11, 2019 USD ($) $ / shares shares	Mar. 20, 2019 USD ($) $ / shares shares	Feb. 13, 2018 shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Conversion of Stock, Shares Issued				0.22148
Stock Issued During Period, Shares, Reverse Stock Splits				7,100,000
Exchange Ratio, Number of Shares Exchanged Per Share				0.0201346
Stock Issued During Period, Shares, New Issues			1,200,000
Gross Proceeds from Issuance of Common Stock | $			$ 3,000,000
Proceeds from Issuance of Common Stock | $			2,500,000			$ 2,540,000
Payments of Stock Issuance Costs | $			$ 320,000
Proceeds from Warrant Exercises | $						$ 180,000
Class of Warrant or Right, Outstanding					43,370,162	43,370,162
Payments for Aggregate Commissions to Underwriters | $		$ 750,000
The April 2019 Offering [Member]
Stock Issued During Period, Shares, New Issues, Excluding Shares Sold to Underwriters		925,455
Shares Issued, Price Per Share | $ / shares		$ 1.10
Proceeds from Issuance or Sale of Equity, Total | $		$ 9,300,000
Net Proceeds from Issuance of Common Stock, Pre-funded Warrants and Common Warrants in Underwritten Offering | $		$ 8,100,000				$ 8,074,000
The September 2019 Offering [Member]
Stock Issued During Period, Shares, New Issues, Excluding Shares Sold to Underwriters	26,124,828
Shares Issued, Price Per Share | $ / shares	$ 0.30
Pre-funded Warrant Price | $ / shares	0.20
Pre-funded Warrant, Accompanying Warrant, Amount Paid Per Share | $ / shares	$ 0.10
Proceeds from Issuance or Sale of Equity, Total | $	$ 8,700,000
Net Proceeds from Issuance of Common Stock, Pre-funded Warrants and Common Warrants in Underwritten Offering | $	7,700,000					7,739,000
Payments for Aggregate Commissions to Underwriters | $	$ 713,000
Warrants in Connection with March 2019 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			84,000
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right			1
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares			$ 3.125
Warrants and Rights Outstanding, Term			5 years
Warrants and Rights Outstanding | $			$ 100,000
Warrants in Connection With the April 2019 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		10,454,546
Warrants and Rights Outstanding | $		$ 333,000
Class of Warrant Right, Number of Pre-funded Warrants Issued During Period		8,165,455
Pre-funded Warrant Price | $ / shares		$ 1
Pre-funded Warrant, Accompanying Warrant, Amount Paid Per Share | $ / shares		$ 0.10
Proceeds from Warrant Exercises | $						$ 800,000
Warrants in Connection With the April 2019 Offering [Member] | Over-Allotment Option [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		1,363,636
Pre-funded Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right	1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	$ 0.10	$ 0.10
Class of Warrant Right, Number of Pre-funded Warrants Issued During Period	4,100,000
Proceeds from Warrant Exercises | $					$ 400,000
Class of Warrant or Right, Outstanding					8,165,455	8,165,455
Class of Warrant or Right, Exercised During Period					4,100,000
Common Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right	1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	$ 0.30	$ 1.10
Warrants and Rights Outstanding, Term	5 years	5 years
Class of Warrant or Right, Exercised During Period					598,067
Underwriter Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right		1
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares		$ 1.375
Class of Warrant or Right, Issued During Period		636,364
Class of Warrant or Right, Period to Expiration		5 years
Class of Warrant or Right, Issued During Period, Fair Value | $		$ 333,000
Warrants in Connection with the September 2019 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	30,666,667
Warrants and Rights Outstanding | $	$ 497,000
Class of Warrant or Right, Exercised During Period	3,558,161
Warrants in Connection with the September 2019 Offering [Member] | Over-Allotment Option [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	4,000,000
Common Stock Warrants [Member]
Proceeds from Warrant Exercises | $					$ 200,000
Underwriter Warrants, September 2019 [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right	1
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	$ 0.375
Warrants and Rights Outstanding | $	$ 497,000
Class of Warrant or Right, Issued During Period	2,115,738
Class of Warrant or Right, Period to Expiration	5 years
Private Vaxart's Stockholders, Warrantholders, and Optionholders [Member]
Ownership Percentage				51.00%
Aviragens Stockholderrs and Optionholders [Member]
Ownership Percentage				49.00%
Reverse Stock Split [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio				11