Note 9 - Share-based Compensation (Details Textual) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018	Dec. 12, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	569,585	624,256
The 2007 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			2,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance	569,585
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares, Authorized and Unissued	925,509
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount	$ 139
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	292 days

Represents the number of shares authorized but not issued.

No definition available.

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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.

+ References

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

Amount of cost to be recognized for option under share-based payment arrangement.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

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)(3)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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