Note 8 - Income Taxes - Summary of Tax Years Subject to Examination in Most Significant Tax Jurisdictions (Details)	12 Months Ended
Dec. 31, 2018
Domestic Tax Authority [Member]
Income tax year under examination	2015 2016 2017 2018
Foreign Tax Authority [Member]
Income tax year under examination	2011 2012 2013 2014 2015 2016 2017 2018

Tax year that remains open to examination under enacted tax laws, in CCYY format.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

Name:	us-gaap_OpenTaxYear
Namespace Prefix:	us-gaap_
Data Type:	us-types:gYearListItemType
Balance Type:	na
Period Type:	duration