Note 9 - Summary of Stock Options (Details Textual) - USD ($)					1 Months Ended			3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 29, 2018	May 30, 2018	Mar. 29, 2018	Dec. 06, 2017	Jun. 30, 2018	Apr. 30, 2018	Jan. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 05, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance					4,209,355			4,209,355			4,209,355		2,694,224
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance					$ 4.76			$ 4.76			$ 4.76		$ 5.80
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											8 years 292 days		8 years 219 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross											2,023,559
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value												$ 30,785
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate								0.00%		0.00%	0.00%	0.00%
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options					$ 6,341,000			$ 6,341,000			$ 6,341,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition											3 years
Nonemployees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate								0.00%		0.00%	0.00%	0.00%
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost		$ 97,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate											0.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance					66,250			66,250			66,250
Restricted Stock [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period					50,000		25,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value					$ 3.58		$ 5.19
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					2 years		1 year
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					0						18,750
The 2006 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance					38,378			38,378			38,378
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					$ 10.49			$ 10.49			$ 10.49
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											4 years 146 days
The 2013 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance					4,170,977			4,170,977			4,170,977
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance					$ 4.71			$ 4.71			$ 4.71
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term											8 years 292 days
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized				914,016
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				4,914,016										4,000,000
Common Stock, Capital Shares Reserved for Future Issuance					486,103			486,103			486,103
The 2013 Plan [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross								570,000		185,250	1,821,171	415,110
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value								$ 1.34		$ 3.31	$ 2.32	$ 2.56
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period								0		7,730	0	7,730
The 2013 Plan [Member] | Nonemployees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross								200,000		5,875	202,388	5,875
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value								$ 1.59		$ 5.11	$ 1.61	$ 5.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period								0		0	0	0
The 2013 Plan [Member] | Restricted Stock [Member] | Board Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period						14,672			9,637
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value						$ 3.44	$ 5.19
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period						14,672	9,637
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value								$ 0.95			$ 1.11
Stock Issued During Period, Shares, Employee Stock Purchase Plans	25,618		20,744
Employee Stock Purchase Plan, Purchase Price	$ 2.31		$ 3.11
Employee Stock Ownership Plan (ESOP), Number of Suspense Shares					335,744			335,744			335,744
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate								0.00%			0.00%