Note 8 - Summary of Stock Options (Details Textual) - USD ($) | Dec. 23, 2016 | Aug. 22, 2016 | May 31, 2017 | Jan. 31, 2017 | Nov. 30, 2016 | Sep. 30, 2016 | Aug. 31, 2016 | Jan. 31, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016 | Dec. 22, 2016 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | | | | | | | | | 2,287,572 | | 2,287,572 | | 1,909,764 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price | | | | | | | | | $ 6.15 | | $ 6.15 | | $ 6.19 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term | | | | | | | | | | | 8 years 299 days | | 9 years 43 days | |
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 | | | | | | | | | $ 4,109,000 | | $ 4,109,000 | | | |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition | | | | | | | | | | | 3 years 14 days | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | | | | | 420,985 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | | | | | | | | | | | 7,730 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | | | | | | | | | | | $ 30,785 | $ 5,000 | | |
Employee Stock Option [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate | | | | | | | | | | | 0.00% | | | |
Two Thousand Five Plan [Member] | | | | | | | | | | | | | | |
Common Stock, Capital Shares Reserved for Future Issuance | | | | | | | | | 1,892 | | 1,892 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | | | | | | | | | 1,892 | | 1,892 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price | | | | | | | | | $ 116.29 | | $ 116.29 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term | | | | | | | | | | | 83 days | | | |
The 2006 Stock Option Plan [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | | | | | | | | | 38,378 | | 38,378 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price | | | | | | | | | $ 10.49 | | $ 10.49 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term | | | | | | | | | | | 5 years 138 days | | | |
The 2013 Plan [Member] | | | | | | | | | | | | | | |
Common Stock, Capital Shares Reserved for Future Issuance | | | | | | | | | 143,110 | | 143,110 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Maximum | | | | | | | | | | | 10.00% | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent | | | | | | | | | | | 110.00% | | | |
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 Authorized, Percentage Increase of Outstanding Common Stock | | 4.00% | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized | 523,209 | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 2,523,209 | | | | | | | | | | | | | 2,000,000 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | | | | | | | | | 2,247,302 | | 2,247,302 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price | | | | | | | | | $ 5.98 | | $ 5.98 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term | | | | | | | | | | | 8 years 324 days | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | | | | | | | | | | 4 years | | | |
The 2013 Plan [Member] | Employees [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | | | | | | | | | $ 3.31 | $ 3.17 | $ 2.56 | $ 3.49 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | | | 185,250 | 28,750 | 415,110 | 158,017 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | | | | | | | | | | | 7,730 | 3,020 | | |
The 2013 Plan [Member] | Nonemployees [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | | | | | | | | | $ 5.11 | | $ 5.11 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | | | | | | | | | 5,875 | 0 | 5,875 | 0 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | | | | | | | | | | | 0 | 0 | | |
The 2013 Plan [Member] | Restricted Stock [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | | | | | | | | | 6,250 | | 6,250 | | | |
The 2013 Plan [Member] | Restricted Stock [Member] | Employees [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period | | | | | | 89 | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | | | | 39,405 | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | | | | | | 39,494 | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | | | | | | | | $ 6.24 | | | | | | |
The 2013 Plan [Member] | Restricted Stock [Member] | Board Members [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | | | 4,797 | | 6,544 | | 5,998 | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 4,797 | | 6,544 | | 5,998 | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | | | $ 7.07 | | $ 5.91 | | $ 7.89 | | | | | | | |
The 2013 Plan [Member] | Restricted Stock [Member] | Consultant [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | | | | 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 | | | | | | $ 7.58 | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | | | | | 1 year | | | | | | | | |
The 2013 Plan [Member] | Holdings Greater Than 10 Percent of Shares Outstanding [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period | | | | | | | | | | | 5 years | | | |
The 2013 Plan [Member] | Quarterly [Member] | Restricted Stock [Member] | Consultant [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | | | | | | | | | | | 18,750 | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage | | | | | | 25.00% | | | | | | | | |