Note 13 - Subsequent Events (Details Textual) - USD ($)	Aug. 06, 2019	Aug. 02, 2019	Jul. 05, 2019	Jul. 11, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 24, 2018
Common Stock, Par or Stated Value Per Share					$ 0.001	$ 0.001
Class of Warrant or Right, Exercise Price of Warrants or Rights							$ 6.75
Subsequent Event [Member]
Development Agreement, Upfront Payment Receivable				$ 1,000,000
Common Stock, Par or Stated Value Per Share		$ 0.001
Subsequent Event [Member] | Private Placement Unit [Member]
Debt Conversion, Converted Instrument, Units	210,887
Number of Common Stock in Each Unit	1
Number of Common Stock Called by Each Unit	1
Debt Instrument Conversion Price, Percentage of Price to Public Offering	3.00%
Number of Warrants in Each Unit	1
Subsequent Event [Member] | Public Offering [Member]
Number of Common Stock in Each Unit		1
Number of Common Stock Called by Each Unit		1
Number of Units Offered to Sale		1,666,667
Common Stock, Par or Stated Value Per Share		$ 0.001
Number of Warrants in Each Unit		1
Unit Offering Price		$ 6
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 6.30
Proceeds from Issuance or Sale of Equity, Gross Amount		$ 10,000,000
Proceeds from Issuance or Sale of Equity, Total		8,760,000
Sale of Units, Offering Expenses, Underwriting Discounts and Commissions		635,000
Underwriting Discounts and Commissions		$ 610,000
Underwriters, Additional Common Shares Authorized to Purchase		250,000
Underwriters, Additional Warrants Authorized to Purchase		250,000
Convertible Promissory Note [Member] | Subsequent Event [Member]
Proceeds from Convertible Debt			$ 625,000
Debt Instrument, Interest Rate, Stated Percentage			14.00%
Debt Conversion, Converted Instrument, Amount	$ 633,000