Note 3 - Share-based Compensation (Details Textual) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) shares
Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total \| $	$ 88.1
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	3 years 109 days
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period \| shares	170
Performance Shares [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total \| $	$ 23.8
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years 109 days
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period \| shares	51,441

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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 (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Number of shares issued under share-based payment arrangement.

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-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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