Note 7 - Stock-based Compensation (Details Textual) - USD ($)		12 Months Ended
Jan. 01, 2022	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 0.89	$ 0.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value		$ 800,000	$ 700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)		0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		1,815,767	1,931,100
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)		$ 0.89	$ 0.68
Share-based Payment Arrangement, Expense		$ 897,260	$ 736,119
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)		10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)		3 years
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 1,100,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		1 year 8 months 12 days
Share-based Payment Arrangement, Expense		$ 100,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		385,267
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)		$ 1.11
Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation (in shares)		6,049
Restricted Stock Units (RSUs) [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)		18 months
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 100,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		2 years 1 month 13 days
Share-based Payment Arrangement, Expense		$ 54,000	$ 18,000
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 (in shares)		580,925
Equity Incentive Plan 2015 [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)	4,076,571

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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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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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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Gross number of share options (or share units) granted during the period.

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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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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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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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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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Number of shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

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

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