Note 1 - Organization and Basis of Presentation (Details Textual)				6 Months Ended
	Apr. 11, 2019 USD ($) $ / shares shares	Mar. 20, 2019 USD ($) $ / shares shares	Feb. 13, 2018 shares	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	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 | $	$ 9,300,000	2,500,000		$ 2,540,000
Payments of Stock Issuance Costs | $		$ 320,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	10,454,546
Stock Issued During Period, Shares, New Issues, Excluding Shares Sold to Underwriters	925,455
Class of Warrant Right, Number of Pre-funded Warrants Issued During Period	8,165,455
Shares Issued, Price Per Share | $ / shares	$ 1.10
Pre-funded Warrant Price | $ / shares	1
Pre-funded Warrant, Accompanying Warrant, Amount Paid Per Share | $ / shares	$ 0.10
Proceeds from Issuance of Common Stock, Net | $	$ 8,100,000
Proceeds from Warrant Exercises | $				$ 652,000
Class of Warrant or Right, Outstanding				12,832,188
Payments for Aggregate Commissions to Underwriters | $	$ 750,000
Number of Reportable Segments				1
Retained Earnings (Accumulated Deficit), Ending Balance | $				$ (104,992,000)		$ (97,989,000)
Notes Payable, Total | $				2,800,000
Cash and Cash Equivalents, at Carrying Value, Ending Balance | $				$ 16,300,000
Over-Allotment Option [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,363,636
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
Pre-funded 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	$ 0.10
Class of Warrant or Right, Outstanding				1,646,364
Common 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	$ 1.10
Class of Warrant or Right, Period to Expiration	5 years
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, Period to Expiration	5 years
Class of Warrant or Right, Issued During Period	636,364
Class of Warrant or Right, Issued During Period, Fair Value | $	$ 333,000
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