Note 8 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 2.16	$ 12.63
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value		$ 0.6	$ 1.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		0	0
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, Award Vesting Period		3 years
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 0.3
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		1 year 21 days
Equity Incentive Plan 2015 [Member]
Percentage of Total Shares Eligible for Plan Reserve, On an Annual Basis		4.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		19,740
Equity Incentive Plan 2015 [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	1,339,215

The percentage of total shares within the plan that may be added to the plan reserve, occurring on an annual basis.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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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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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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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

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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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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- Definition

Number of share options (or share units) exercised during the current period.

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