Note 3 - Share-based Compensation (Details Textual) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($) shares	Jun. 30, 2017 USD ($) shares
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 59.0	$ 59.0
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		3 years 292 days
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period \| shares	5,514	14,623
Performance Shares [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 13.3	$ 13.3
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years 146 days

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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