Note 4 - Stockholders' Equity (Details Textual) - USD ($) | 1 Months Ended | 3 Months Ended | 12 Months Ended |
Jan. 31, 2020 | Jul. 31, 2019 | Feb. 28, 2019 | Aug. 31, 2017 | Dec. 31, 2016 | May 31, 2016 | Mar. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018 |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period | | | | | | | | 10 years | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | | | | | | | | 7,441,532 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | | | | | | | | $ 3.45 | $ 9.40 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value | | | | | | | | $ 671,100 | $ 205,000 |
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount | | | | | | | | $ 155,000 | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition | | | | | | | | 219 days | |
Additional Research and Development Expense Due to Modifications | | | | | | | $ 102,000 | | |
Proceeds from Warrant Exercises | | | | | | | | $ 236 | |
Proceeds from Issuance or Sale of Equity, Net of Issuance Costs | | | | | | | | $ 6,552,842 | 1,828,000 |
Underwritten Public Offering [Member] | | | | | | | | | |
Number of Prefunded Units Sold | | 2,361,462 | | | | | | | |
Number of Units Sold | | 416,315 | | | | | | | |
Unit Price | | $ 2.70 | | | | | | | |
Proceeds from Issuance or Sale of Equity, Total | | $ 7,500,000 | | | | | | | |
Number of Common Stock in Each Unit | | 1 | | | | | | | |
Number of Short-term Warrants in Each Unit | | 1 | | | | | | | |
Number of Long-term Warrants in Each Unit | | 1 | | | | | | | |
Number of Prefunded Warrants in Each Prefunded Unit | | 1 | | | | | | | |
Number of Short-term Warrants in Each Prefunded Unit | | 1 | | | | | | | |
Number of Long-term Warrants in Each Prefunded Unit | | 1 | | | | | | | |
Proceeds from Issuance or Sale of Equity, Net of Issuance Costs | | $ 6,600,000 | | | | | | | |
Private Placement [Member] | | | | | | | | | |
Conversion of Stock, Shares Converted | | 800,000 | | | | | | | |
Stock Issued During Period, Shares, Conversion of Convertible Securities | | 155,496 | | | | | | | |
Private Placement [Member] | Series A 4.5% Convertible Preferred Stock [Member] | | | | | | | | | |
Stock Issued During Period, Shares, New Issues | | | | | 200,000 | | | | |
Preferred Stock, Dividend Rate, Percentage | | | | | 4.50% | | | | |
Convertible Preferred Stock, Issuable Upon Conversion of All Shares | | | | | 38,873 | | | | |
Over-Allotment Option [Member] | | | | | | | | | |
Underwriters, Additional Common Shares Authorized to Purchase | | 416,666 | | | | | | | |
Underwriters, Additional Warrants Authorized to Purchase | | 416,666 | | | | | | | |
Stock Purchase Warrants [Member] | | | | | | | | | |
Class of Warrant or Right, Issued During Period | | | 25,000 | 112,500 | | 87,309 | | | |
Class of Warrant or Right, Outstanding | | | | | | | | 149,136 | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | | | $ 6 | | | | | $ 2.70 | |
Class of Warrant or Right, Granted During Period, Weighted Average Grant Date Fair Value | | | $ 3.80 | | | | | | |
Class of Warrant or Right, Vesting Percentage on Grant | | | 25.00% | | | | | | |
Class of Warrant or Right, Vesting Percentage on Completion of Initial Services | | | 75.00% | | | | | | |
Warrants and Rights Outstanding, Term | | | 2 years 182 days | | | | | | |
Stock Purchase Warrants [Member] | Subsequent Event [Member] | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ 1.36 | | | | | | | | |
Proceeds from Warrant Exercises | $ 7,600,000 | | | | | | | | |
Class of Warrant or Right, Exercised During Period | 5,555,554 | | | | | | | | |
Class of Warrant or Right, Exercised During Period, Exercise Price | $ 1.36 | | | | | | | | |
Stock Purchase Warrants [Member] | Measurement Input, Expected Dividend Rate [Member] | | | | | | | | | |
Warrants and Rights Outstanding, Measurement Input | | | 0 | | | | | | |
Stock Purchase Warrants [Member] | Measurement Input, Risk Free Interest Rate [Member] | | | | | | | | | |
Warrants and Rights Outstanding, Measurement Input | | | 0.025 | | | | | | |
Stock Purchase Warrants [Member] | Measurement Input, Price Volatility [Member] | | | | | | | | | |
Warrants and Rights Outstanding, Measurement Input | | | 1.1 | | | | | | |
Short-term Warrants [Member] | Underwritten Public Offering [Member] | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | | $ 2.70 | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | | 3,194,443 | | | | | | | |
Long-term warrants [Member] | Underwritten Public Offering [Member] | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | | $ 2.70 | | | | | | | |
Warrants and Rights Outstanding, Term | | 5 years | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | | 3,194,443 | | | | | | | |
Prefunded Warrants [Member] | | | | | | | | | |
Proceeds from Warrant Exercises | | | | | | | | $ 200 | |
Prefunded Warrants [Member] | Underwritten Public Offering [Member] | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | | $ 0.0001 | | | | | | | |
Equity Classified Warrants [Member] | Underwritten Public Offering [Member] | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | | $ 3.375 | | | | | | | |
Warrants and Rights Outstanding, Term | | 5 years | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | | 222,223 | | | | | | | |
Replacement Stock Purchase Warrants [Member] | Subsequent Event [Member] | | | | | | | | | |
Class of Warrant or Right, Outstanding | 5,555,554 | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ 1.23 | | | | | | | | |
Stock Purchase Warrants With 2 Year Term [Member] | Subsequent Event [Member] | | | | | | | | | |
Class of Warrant or Right, Outstanding | 2,777,777 | | | | | | | | |
Warrants and Rights Outstanding, Term | 2 years | | | | | | | | |
Stock Purchase Warrants With 5 Year Term [Member] | Subsequent Event [Member] | | | | | | | | | |
Class of Warrant or Right, Outstanding | 2,777,777 | | | | | | | | |
Warrants and Rights Outstanding, Term | 5 years | | | | | | | | |
Placement Agent Stock Purchase Warrants [Member] | Subsequent Event [Member] | | | | | | | | | |
Class of Warrant or Right, Outstanding | 444,445 | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ 1.70 | | | | | | | | |
Warrants and Rights Outstanding, Term | 5 years | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | | | | | | | | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition | | | | | | | | 182 days | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding | | | | | | | | $ 5,400 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | | | | | | | | 13,900 | $ 50,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | | | $ 10,400 | |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised | | | | | | | | 1,127 | 0 |
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount | | | | | | | | $ 15,000 | |
Restricted Stock [Member] | | | | | | | | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition | | | | | | | | 182 days | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding | | | | | | | | $ 7,900 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | | | 18,500 | |
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount | | | | | | | | $ 47,500 | |