Note 11 - Stock-based Compensation - Stock Options Granted (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Weighted average grant date fair value (in dollars per share)	$ 12.63	$ 5.31

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

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

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration