Note 3 - Fair Value Measurements - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost	$ 13,973	$ 20,991
Unrealized Gains
Unrealized Losses	(4)	(20)
Fair Value	13,969	20,971
US Government Agencies Debt Securities [Member]
Amortized Cost	13,973	20,991
Unrealized Gains
Unrealized Losses	(4)	(20)
Fair Value	$ 13,969	$ 20,971

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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