Note 3 - Stock-based Compensation Plans and Warrants (Details Textual) - USD ($)				1 Months Ended		3 Months Ended					9 Months Ended		12 Months Ended		54 Months Ended
	Jul. 10, 2019	Jan. 01, 2019	Dec. 18, 2009	May 31, 2017	Jun. 30, 2014	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	[1]	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Jun. 09, 2014	Jun. 14, 2014	Jun. 10, 2014
Share-based Payment Arrangement, Expense						$ 165,000				$ 123,000	$ 410,000	$ 350,000
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
Retained Earnings [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
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]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,200,000					1,200,000					1,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period											7,386
Two Thousand Nineteen Equity Incentive Plan [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] | 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
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period											674,987
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.