Represents the aggregate offering price increase during period.

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Represents the maximum aggregate offering price.

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Represents the percentage of common stock voting right.

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Represents the fair value of common stock as a percentage of option exercise price.

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The cash inflow from the issuance of common stock, net of issuance costs.

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Represents the shared-based compensation arrangement by share-based payment award equity instrument other than options outstanding.

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Represents the percent of share-based payment award number of shares authorized.

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Represents the stock option plan option reserve annual increase as percentage of outstanding shares allowed.

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The cash outflow for cost incurred directly with the issuance of an equity security.

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The cash inflow associated with the amount received from entity's first offering of stock to the public.

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The cash inflow from the additional capital contribution to the entity.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Per share or per unit amount of equity securities issued.

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Number of new stock issued during the period.

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Note 11 - Stockholders' Equity (Details Textual) - USD ($)							1 Months Ended				9 Months Ended	12 Months Ended
	Jan. 01, 2020	May 09, 2019	Nov. 14, 2018	Aug. 07, 2018	Jul. 16, 2018	Jun. 21, 2016	Aug. 07, 2018	Nov. 30, 2009	Feb. 29, 2008	Aug. 31, 2006	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2011	Jan. 31, 2020
Proceeds from Issuance of Common Stock												$ 1,233,000	$ 81,525,000	$ 15,694,000
Employee Stock Purchase Plan, Shares Issued, Weighted Average Fair Value												$ 2.33	$ 1.51	$ 2.59
2006 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized										342,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized								1,400,000	375,000
2006 Equity Incentive Plan [Member] \| Minimum [Member]
Common Stock Voting Rights Percentage										10.00%
2006 Equity Incentive Plan [Member] \| Maximum [Member]
Fair Value of Common Stock as Percentage of Option Exercise Price										110.00%
2011 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Outstanding															1,900,000
Stock Option Plan Option Reserve Annual Increase as Percentage of Outstanding Shares Allowed															4.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period															4 years
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant												1,950,652
2011 Equity Incentive Plan [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	3,182,924
2011 Equity Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period															10 years
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized												655,420
Share-based Payment Award, Number of Shares Authorized															2.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant												203,469
Employee Stock Purchase Plan (ESPP) [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized																1,591,462
Public Offering [Member]
Proceeds from Issuance Initial Public Offering						$ 40,000,000						$ 80,000,000
Underwritten Public Offering [Member]
Stock Issued During Period, Shares, New Issues			14,603,173	1,090,909	7,272,727		8,363,636
Shares Issued, Price Per Share			$ 3.15	$ 2.75	$ 2.75		$ 2.75
Proceeds from Issuance of Common Stock			$ 46,000,000				$ 23,000,000
Proceeds from Issuance of Common Stock, Net			$ 43,100,000				$ 21,700,000
ATM Agreement [Member]
Stock Issued During Period, Shares, New Issues												500,000
Proceeds from Issuance of Common Stock												$ 1,200,000
Aggregate Offering Price, Increase During Period		$ 40,000,000
Payments of Stock Issuance Costs												$ 32,000
Aggregate Offering Price, Maximum											$ 45,300,000
ATM Agreement 2016 [Member]
Stock Issued During Period, Shares, New Issues													4,400,000	5,400,000
Proceeds from Issuance of Common Stock, Net													$ 16,800,000	$ 15,700,000
Payments of Stock Issuance Costs													$ 400,000	$ 500,000