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Note 6 - Share-based Compensation - Summary of Significant Assumptions for Share-based Compensation Awards (Details) - $ / shares | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Expected award life (Year) |  |  |  | 5 years |
Stock Appreciation Rights (SARs) [Member] |  |  |  |  |
Exercise price (in dollars per share) |  | $ 23.59 | $ 16.97 | $ 23.59 | $ 16.97
Market price (in dollars per share) |  |  |  | $ 23.59 | $ 16.97
Risk free interest rate | [1] |  |  | 2.60% | 1.90%
Expected award life (Year) | [2] |  |  | 3 years | 5 years
Expected volatility | [3] |  |  | 35.40% | 36.60%
Expected dividend yield | [4] |  |  | 1.60% | 2.10%
Employee Stock Option [Member] |  |  |  |  |
Exercise price (in dollars per share) |  | 18.86 | 21.63 | $ 18.86 | $ 21.63
Market price (in dollars per share) |  | $ 18.86 | $ 21.63 |  |
Risk free interest rate | [1] | 2.70% | 1.80% |  |
Expected award life (Year) | [2] | 3 years | 5 years |  |
Expected volatility | [3] | 35.40% | 37.20% |  |
Expected dividend yield | [4] | 2.10% | 1.80% |  |
Employee Stock Option [Member] | Minimum [Member] |  |  |  |  |
Exercise price (in dollars per share) |  | $ 18.86 | $ 16.97 | 18.86 | 16.97
Market price (in dollars per share) |  |  |  | $ 18.86 | $ 16.97
Risk free interest rate | [1] |  |  | 2.60% | 1.80%
Expected award life (Year) | [2] |  |  | 3 years | 5 years
Expected volatility | [3] |  |  | 35.40% | 36.60%
Expected dividend yield | [4] |  |  | 1.60% | 1.80%
Employee Stock Option [Member] | Maximum [Member] |  |  |  |  |
Exercise price (in dollars per share) |  | $ 24.28 | $ 21.63 | $ 24.28 | $ 21.63
Market price (in dollars per share) |  |  |  | $ 24.28 | $ 21.63
Risk free interest rate | [1] |  |  | 2.90% | 2.40%
Expected award life (Year) | [2] |  |  | 10 years | 10 years
Expected volatility | [3] |  |  | 42.10% | 41.40%
Expected dividend yield | [4] |  |  | 2.10% | 2.10%
[1] | The risk-free interest rate is based on the yield of a U.S. treasury bond with a similar maturity as the expected life of the awards.
[2] | The expected life in years for awards granted was based on the historical exercise patterns experienced by the Company when the award is made.
[3] | The determination of expected stock price volatility for awards granted in each of the periods ending September 30, 2018 and 2017 was based on historical Superior common stock prices over a period commensurate with the expected life.
[4] | The dividend yield assumption is based on the history and expectation of the Company's dividend payouts.

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- Definition Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award. + References No definition available. + 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=109197908&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=109197908&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=109197908&loc=d3e5070-113901 + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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=109197908&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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