Note 6 - Employee Benefit Plans - Weighted-average Assumptions to Value Share-based Awards Granted (Details) - $ / shares	12 Months Ended
Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Restricted Stock Units (RSUs) [Member]
Dividend yield	0.00%	1.60%	1.00%
Employee Stock Purchase Plan [Member]
Dividend yield	0.50%	1.30%	1.10%
Expected volatility	67.10%	46.40%	39.00%
Risk-free interest rate	1.10%	2.20%	1.70%
Expected term (Year)	6 months	6 months	6 months
Weighted-average grant date fair value per share (in dollars per share)	$ 6.01	$ 5.35	$ 5.90

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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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

Expected term of 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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