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Note 11 - Share-based Compensation - Summary of Significant Assumptions for Share-based Compensation Awards (Details) - $ / shares | 12 Months Ended
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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

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- Definition 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. + 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 (c)(2)(iii)(3) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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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. + 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 (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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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. + 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 (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + 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 (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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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. + 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 (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
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