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Note 13 - Equity Incentive Plans (Details Textual) - USD ($)		1 Months Ended	12 Months Ended
	Apr. 23, 2019	Nov. 30, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant			295,180	200,650
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance			1,811,652	865,163	304,850
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance			$ 2.74	$ 8.13	$ 9.50
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				2,013
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount			$ 700,000
Common Stock [Member]
Share Price			$ 0.35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				2,013
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance			1,811,652
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance			$ 2.74
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term			8 years 32 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value			$ 14,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number			582,085
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price			$ 6.18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term			5 years 138 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value			$ 3,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value			$ 774,000	$ 332,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period			0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 0.48	$ 3.59
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition			2 years 156 days
The 2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant						0
The 2016 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	0
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		10 years
The 2019 Plan [Member]
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	1,600,000