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Note 1 - Summary of Significant Accounting Policies - Fair Value Assumptions (Details) - Employee Stock Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Expected volatility	27.70%		29.70%
Risk-free interest rate	2.70%		0.90%
Exercise price (in dollars per share)	$ 31.20		$ 22.02
Expected term (Year)	6 years		5 years
Weighted-average grant-date fair value (in dollars per share)	$ 10.15		$ 6.11
Minimum [Member]
Expected volatility		27.40%
Risk-free interest rate		1.56%
Exercise price (in dollars per share)		$ 27.05
Expected term (Year)		2 years 255 days
Weighted-average grant-date fair value (in dollars per share)		$ 5.59
Maximum [Member]
Expected volatility		29.10%
Risk-free interest rate		1.84%
Exercise price (in dollars per share)		$ 28.70
Expected term (Year)		5 years 292 days
Weighted-average grant-date fair value (in dollars per share)		$ 8.51

X

- Definition

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

+ References

No definition available.

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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

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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

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

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-Publisher FASB
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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

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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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