Note 6 - Employee Stock Benefit Plans (Details Textual) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 26, 2020 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (in shares)	28,455
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares)	334,821
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share) \| $ / shares	$ 10.02
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value \| $	$ 2.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	2 years 1 month 6 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	778,903
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	575,830
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	63,283
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)	1,467,448
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding \| $	$ 24.7
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms (Year)	1 year 6 months
Restricted Stock Units (RSUs) [Member] \| Vesting Over One Year Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	1 year
Restricted Stock Units (RSUs) [Member] \| Vesting Over Four Year Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	200,249
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	39,075
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	99,933
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)	425,435
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding \| $	$ 7.1
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 9 months 18 days
Equity Based Performance Stock Units Granted in 2020, 2019, 2018, and 2017 [Member] \| Vest on the Third Anniversary of Awards Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	100.00%
Minimum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Shares Available for Issue	25.00%
Maximum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Shares Available for Issue	200.00%
Equity Incentive Plan 2005 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)	1,664,421
Equity Incentive Plan 2005 [Member] \| Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years
Equity Incentive Plan 2005 [Member] \| Minimum [Member] \| Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	1 year
Equity Incentive Plan 2005 [Member] \| Maximum [Member] \| Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)	797,727
Percentage of Fair Value to Determine Price of Common Stock	85.00%
Stock Issued During Period, Shares, New Issues (in shares)	113,610

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Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of new stock issued during the period.

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