Note 6 - Employee Stock Benefit Plans (Details Textual) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 27, 2021 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)	192,432
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number (in shares)	70,203
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share) \| $ / shares	$ 10.04
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value \| $	$ 2.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	2 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	204,449
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	409,690
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	4,406
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)	1,205,125
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding \| $	$ 49.2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms (Year)	1 year 7 months 6 days
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)	92,719
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	116,219
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period (in shares)	3,182
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)	398,753
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding \| $	$ 16.3
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)	1,390,895
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)	668,704
Percentage of Fair Value to Determine Price of Common Stock	85.00%
Stock Issued During Period, Shares, New Issues (in shares)	0

Percentage of the Fair Value to Determine the price of common stock.

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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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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit 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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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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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