Note 12 - Stock Incentive Plans (Details Textual)	3 Months Ended
Mar. 31, 2019
Restricted Stock Units (RSUs) [Member] \| Share-based Compensation Awards Issued in 2018, Vesting Period [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Performance Share Units [Member] \| Awards Granted in 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Equal Installments	3

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration