Note 10 - Summary of Stock Options (Details Textual) - USD ($)					1 Months Ended				3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 28, 2019	Mar. 29, 2019	Jan. 01, 2019	Jun. 08, 2018	Jun. 30, 2019	Apr. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance					5,314,375				5,314,375		5,314,375		4,014,475
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance					$ 3				$ 3		$ 3		$ 4.56
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											8 years 219 days		7 years 146 days
Stock Issued During Period, Shares, Restricted Stock Award, Gross				100,000			27,473
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance					393,051				393,051		393,051
Shares Issued, Price Per Share				$ 2.56			$ 0.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross											2,335,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate									0.00%	0.00%	0.00%	0.00%
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate											0.00%
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount					$ 4,143,620				$ 4,143,620		$ 4,143,620
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition											2 years 138 days
Consultant [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross					25,000
Director [Member]
Stock Issued During Period, Shares, Restricted Stock Award, Gross						52,791
Director [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value						$ 0.91
Nonemployees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate										0.00%	0.00%	0.00%
The 2006 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance					10,434				10,434		10,434
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant					0				0		0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance					$ 10.05				$ 10.05		$ 10.05
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											3 years 215 days
The 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance					5,303,941				5,303,941		5,303,941
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance					$ 3				$ 3		$ 3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											8 years 233 days
Common Stock, Capital Shares Reserved for Future Issuance					904,651				904,651		904,651
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized			2,043,142
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			6,957,158										4,914,016
The 2013 Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period								364,072
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period									2,271		2,271
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period											0
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures, Total											0
The 2013 Plan [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross									190,000	570,000	2,307,500	1,821,171
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value									$ 0.33	$ 1.34	$ 1.18	$ 2.32
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period									0	0	0	0
The 2013 Plan [Member] | Nonemployees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross									27,500	200,000	27,500	202,388
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value									$ 1.22	$ 1.59	$ 1.22	$ 1.61
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period									0	0	0	0
2017 Employee Stock Purchase Plan [Member]
Stock Issued During Period, Shares, Employee Stock Purchase Plans	60,740	43,759
Shares Issued, Price Per Share	$ 0.32	$ 0.80
Employee Stock Ownership Plan (ESOP), Number of Suspense Shares					151,820				151,820		151,820
Employee Stock Ownership Plan (ESOP), Weighted Average Purchase Price of Shares Purchased									$ 0.95	$ 0.95	$ 0.68	$ 1.11
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate									0.00%	0.00%	0.00%	0.00%