Note 7 - Share-based Compensation - Fair Value Assumptions (Details) - Share-based Payment Arrangement, Option [Member] - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Fair value of ordinary share (in dollars per share)		$ 34
Risk-free interest rate		2.28%
Expected term (years) (Year)		5 years 182 days
Expected volatility	60.00%	60.00%
Expected dividend yield	0.00%	0.00%
Contractual life (years) (Year)	10 years	10 years
Minimum [Member]
Fair value of ordinary share (in dollars per share)	$ 24.87
Risk-free interest rate	2.73%
Expected term (years) (Year)	5 years 328 days
Maximum [Member]
Fair value of ordinary share (in dollars per share)	$ 26.09
Risk-free interest rate	2.89%
Expected term (years) (Year)	6 years 73 days

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.

+ References

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

Price of a single share of a number of saleable stocks of a company.

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No definition available.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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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=116856206&loc=d3e5070-113901

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-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

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