Represents expected volatility rate period for share based payment award by share based payment.

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Fair value of non-vested equity-based payment instruments, excluding stock (or unit) options, vested.

+ References

No definition available.

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Represents historical volatility for fair value assumptions for share-based payment award by share based compensation.

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No definition available.

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Percent of shares that may be issued in accordance with the plan as a proportion of outstanding awards.

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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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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 equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

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

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

+ References

No definition available.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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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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Note 7 - Stock-based Compensation (Details Textual) - USD ($)					3 Months Ended
	Feb. 08, 2021	Mar. 25, 2020	Apr. 01, 2019	Feb. 25, 2019	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Share-based Payment Arrangement, Expense					$ 1,505,000	$ 1,113,000
Share-based Payment Arrangement, Option [Member]
Share-based Payment Arrangement, Expense					9,000	61,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value					24,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value					24,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value					$ 3,300,000	$ 3,000,000.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)					3 years 9 months 18 days
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 16,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					0
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value					$ 20,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value					$ 2,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)					8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)						0
Performance Shares [Member] \| Management Performance Bonus Plan 2017 [Member]
Share-based Payment Arrangement, Expense					$ 0	$ 0
Restricted Stock [Member]
Share-based Payment Arrangement, Expense					1,400,000	394,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 17,000,000.0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					3 years 2 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Fair Value					$ 2,200,000	1,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value					$ 2,600,000	813,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)					52,616
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)					68,365
Performance-based Restricted Stock [Member]
Share-based Payment Arrangement, Expense					$ 186,000	189,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)					20,285
Market-based Restricted Stock [Member]
Share-based Payment Arrangement, Expense					$ 285,000	$ 469,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 2,000,000.0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year 6 months
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	30,616	109,140	29,604	94,247	146,250
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	231,268				231,268
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance	68.00%	78.00%	69.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	0.10%	0.30%	2.50%
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	2 years		2 years
Market-based Restricted Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards	200.00%	200.00%	200.00%
Market-based Restricted Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards	0.00%	0.00%
Market-based Restricted Stock First Issuance [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total							$ 3,100,000