v3.19.2

Note 2 - Investments and Fair Value Measurement - Summary of Cash, Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Amortized Cost	$ 91,546	$ 105,715
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	91,546	105,715
Cash and Cash Equivalents [Member]
Amortized Cost	65,071	87,975
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	65,071	87,975
Cash and Cash Equivalents [Member] | Cash [Member]
Amortized Cost	3,018	2,037
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	3,018	2,037
Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Amortized Cost	286	1,436
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	286	1,436
Cash and Cash Equivalents [Member] | Commercial Paper [Member]
Amortized Cost	61,767	74,321
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	61,767	74,321
Cash and Cash Equivalents [Member] | U.S. Government Agency Securities [Member]
Amortized Cost		10,181
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value		10,181
Marketable Securities [Member]
Amortized Cost		17,740
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value		17,740
Marketable Securities [Member] | Commercial Paper [Member]
Amortized Cost	26,475	16,243
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	$ 26,475	16,243
Marketable Securities [Member] | U.S. Government Agency Securities [Member]
Amortized Cost		1,497
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value		$ 1,497

X

- Definition

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

+ References

No definition available.

+ Details

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

X

- 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=118939692&loc=d3e27161-111563

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X

- 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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X

- Definition

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+ References

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X

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X

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