Note 11 - Share-based Compensation - Summary of Significant Assumptions for Share-based Compensation Awards (Details) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Option [Member]
Weighted average fair value per share at grant date (in dollars per share)	$ 2.36	$ 3.96	$ 5.93
Share-based Payment Arrangement, Option [Member] \| Minimum [Member]
Risk free interest rate	0.10%	1.70%	2.60%
Expected award life (years) (Year)	3 years	3 years	3 years
Expected volatility	35.60%	34.20%	35.40%
Expected dividend yield	1.90%	2.30%	1.60%
Share-based Payment Arrangement, Option [Member] \| Maximum [Member]
Risk free interest rate	1.40%	2.50%	2.90%
Expected award life (years) (Year)	10 years	10 years	10 years
Expected volatility	61.50%	38.80%	42.10%
Expected dividend yield	5.30%	2.50%	2.10%
Stock Appreciation Rights (SARs) [Member]
Risk free interest rate		2.40%	2.60%
Expected award life (years) (Year)	3 years	3 years	3 years
Expected volatility		34.80%	38.10%
Expected dividend yield		2.30%	1.60%
Weighted average fair value per share at grant date (in dollars per share)	$ 2.18	$ 3.97	$ 6.06

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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 estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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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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- Definition

Expected term of 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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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