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Note 6 - Share-based Compensation (Details Textual) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) shares	Dec. 31, 2020	Dec. 31, 2019
Number Of Active Stock Incentive Plans	1
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	3 years
Performance Shares [Member]
Restricted Stock Units and Performance Share Award Target Level, Percentage	100.00%
Performance Awards Issued Multiplier		200.00%	126.00%
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number At Target Level Of Performance (in shares) | shares	116,000
Performance Shares [Member] | Minimum [Member]
Performance Awards Issued Multiplier	0.00%
Performance Shares [Member] | Maximum [Member]
Performance Awards Issued Multiplier	200.00%
Restricted Stock Units and Performance Stock Awards [Member]
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount | $	$ 5
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	2 years

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The number of active stock incentive plans.

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- Definition

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- Definition

The number of non-vested equity-based payment instruments at a target level of performance, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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- Definition

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.

+ References

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 (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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