Note 3 - Stock-based Compensation Plans and Warrants (Details Textual) - USD ($)				1 Months Ended		3 Months Ended				6 Months Ended		12 Months Ended		54 Months Ended
	Jul. 10, 2019	Jan. 01, 2019	Dec. 18, 2009	May 31, 2017	Jun. 30, 2014	Jun. 30, 2019	Mar. 31, 2019	[1]	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Jun. 09, 2014	Jun. 14, 2014	Jun. 10, 2014
Share-based Payment Arrangement, Expense						$ 122,000			$ 122,000	$ 245,000	$ 227,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance						492,500				492,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period										0
Current Period Reclassification Adjustment		$ 865,000					$ 865,000
Reclassification of Warrant Liability to Additional Paid-in Capital [Member]
Current Period Reclassification Adjustment						$ 24,000				$ 865,000
Gains from Revaluating Warrants												$ 1,500,000	$ 500,000
2017 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				362,500
Warrant Term				5 years
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 14.94		$ 14.59				$ 14.59
Warrants and Rights Outstanding				$ 2,900,000
Common Stock [Member]
Current Period Reclassification Adjustment
Additional Paid-in Capital [Member]
Current Period Reclassification Adjustment						$ 24,000	$ 2,896,000
Additional Paid-in Capital [Member] | Reclassification of Warrant Liability to Additional Paid-in Capital [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 2,000,000
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense										$ 0	$ 0
Two Thousand Nine Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			850,000												850,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period					45,235
Two Thousand Nine Equity Incentive Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period														297,265
Two Thousand Nine Equity Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period			10 years
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period														507,500
Two Thousand Nine Equity Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period			2 years
Twenty Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized																675,000
Two Thousand Nineteen Equity Incentive Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,200,000
Two Thousand Nineteen Equity Incentive Plan [Member] | Subsequent Event [Member] | Outside Director [Member] | Accrues Yearly [Member]
Salary and Wage, Officer, Excluding Cost of Good and Service Sold	$ 50,000
Share-based Payment Arrangement, Expense	25,000
Two Thousand Nineteen Equity Incentive Plan [Member] | Subsequent Event [Member] | Outside Director [Member] | Accrues Quarterly [Member]
Salary and Wage, Officer, Excluding Cost of Good and Service Sold	12,500
Share-based Payment Arrangement, Expense	$ 6,250
Two Thousand Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized						675,000				675,000
Two Thousand Fourteen Equity Incentive Plan [Member] | Directors, Consultants and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period										673,466
Two Thousand Fourteen Equity Incentive Plan [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period										15,312

[1] A cumulative effect adjustment of $2,031 thousand was recognized as of January 1, 2019, upon adoption of ASU 2017-11