Note 8 - Fair Value Measurements - Fair Value Measurements of Assets and Liabilities on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative liabilities	$ 3
Fair Value, Inputs, Level 1 [Member]
Derivative liabilities
Fair Value, Inputs, Level 2 [Member]
Derivative liabilities	3
Fair Value, Inputs, Level 3 [Member]
Derivative liabilities
Money Market Funds [Member]
Money market mutual funds	773	$ 2,998
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Money market mutual funds	773	2,998
Money Market Funds [Member] \| Fair Value, Inputs, Level 2 [Member]
Money market mutual funds
Money Market Funds [Member] \| Fair Value, Inputs, Level 3 [Member]
Money market mutual funds
US Government-sponsored Enterprises Debt Securities [Member]
Short-term securities	1,785	786
Long-term securities	19,512	21,258
US Government-sponsored Enterprises Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Short-term securities
Long-term securities
US Government-sponsored Enterprises Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Short-term securities	1,785	786
Long-term securities	19,512	21,258
US Government-sponsored Enterprises Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Short-term securities
Long-term securities
Corporate Debt Securities [Member]
Short-term securities	25,579	18,430
Long-term securities	50,896	56,398
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Short-term securities
Long-term securities
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Short-term securities	25,579	18,430
Long-term securities	50,896	56,398
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Short-term securities
Long-term securities

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (available-for-sale), classified as noncurrent.

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

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