v3.8.0.1

Note 12 - Stock-based Compensation - Assumptions to Calculate Fair Value of Each Employee Stock Option (Details) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Expected term (in years) (Year) | 5 years 255 days |  |
Expected volatility | 73.00% | 80.00% | 72.00%
Expected dividend rate | 0.00% | 0.00% | 0.00%
Minimum [Member] |  |  |
Expected term (in years) (Year) | 5 years 255 days | 5 years 91 days | 5 years 91 days
Risk-free interest rate | 1.82% | 1.24% | 1.35%
Expected volatility | 73.00% | 80.00% | 72.00%
Expected dividend rate | 0.00% | 0.00% | 0.00%
Maximum [Member] |  |  |
Expected term (in years) (Year) | 5 years 255 days | 6 years 91 days | 6 years 91 days
Risk-free interest rate | 2.09% | 1.47% | 1.82%
Expected volatility | 73.00% | 80.00% | 72.00%
Expected dividend rate | 0.00% | 0.00% | 0.00%

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- Definition Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + 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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 + Details
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- Definition The maximum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + Details
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- Definition The minimum risk-free interest rate assumption that is used in valuing an option on its own shares. + References No definition available. + 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://www.xbrl.org/2003/role/presentationRef -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=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -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=27013229&loc=d3e301413-122809 + Details
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