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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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Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

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

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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 9 - Stock-based Compensation (Details Textual) - USD ($)					12 Months Ended
	Feb. 08, 2021	Mar. 25, 2020	Apr. 01, 2019	Feb. 25, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2020	May 31, 2017	Dec. 31, 2013
Share-based Payment Arrangement, Expense					$ 5,981,000	$ 3,043,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)					3 years 7 months 28 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)					930,854	429,399	279,919
Share-based Payment Arrangement, Expense					$ 3,000,000.0	$ 1,200,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 16,300,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					3 years 3 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Fair Value					$ 15,300,000	5,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value					$ 4,500,000	$ 1,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)					717,267	309,218
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)					$ 20.88	$ 17.15
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)					208,858	125,818
Restricted Stock [Member] \| Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)		34,154
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 9.18
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)					844,455	1,570,455	2,043,402
Share-based Payment Arrangement, Expense					$ 119,000	$ 370,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value					32,000,000.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value					31,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value					$ 13,100,000	$ 7,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)					3 years 8 months 12 days	5 years
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 29,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					9 months 18 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)					686,001	737,497	964,997
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					0	0
Performance-based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)					0	0
Share-based Payment Arrangement, Expense					$ 760,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)		82,805			82,805
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 9.18			$ 9.18
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)					82,805
Performance-based Restricted Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards		0.00%
Performance-based Restricted Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards		125.00%
Market-based Restricted Stock [Member]
Share-based Payment Arrangement, Expense					$ 2,100,000	$ 1,500,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 674,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)		109,140	29,604	94,247
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance		78.00%	69.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		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] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	231,268
Market-based Restricted Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards		0.00%
Market-based Restricted Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Awards		200.00%	200.00%
Market-based Restricted Stock First Issuance [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 3,100,000
Market-based Restricted Stock Second Issuance [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total					$ 1,200,000
The 2013 Performance Incentive Plan [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)									5,000,000.0	4,100,000	3,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)					1,400,000
The 2013 Performance Incentive Plan [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares)					1,200,000
All Other Unapproved Compensation Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares)					123,000
Management Performance Bonus Plan 2017 [Member] \| Performance Shares [Member]
Share-based Payment Arrangement, Expense					$ 0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value					26,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value					$ 1,300,000	$ 3,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)					0	0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					1 year
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)								1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price (in dollars per share)								$ 1.64
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares (in shares)							999,997	999,997