Note 2 - Investments and Fair Value Measurement - Summary of Cash, Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost	$ 43,023	$ 66,137
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	43,023	66,137
Cash and Cash Equivalents [Member]
Amortized Cost	19,973	14,684
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	19,973	14,684
Cash and Cash Equivalents [Member] \| Cash [Member]
Amortized Cost	1,357	1,957
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,357	1,957
Cash and Cash Equivalents [Member] \| Money Market Funds [Member]
Amortized Cost	1,415	598
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,415	598
Cash and Cash Equivalents [Member] \| U.S. Government Agency Securities [Member]
Amortized Cost		14,268
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		14,268
Cash and Cash Equivalents [Member] \| Commercial Paper [Member]
Amortized Cost	12,199	12,129
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	12,199	12,129
Marketable Securities [Member]
Amortized Cost	23,050	51,453
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	23,050	51,453
Marketable Securities [Member] \| U.S. Government Agency Securities [Member]
Amortized Cost	5,002
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	5,002
Marketable Securities [Member] \| Commercial Paper [Member]
Amortized Cost	9,197	27,131
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	9,197	27,131
Marketable Securities [Member] \| US Government Agencies Debt Securities [Member]
Amortized Cost	13,853
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 13,853
Marketable Securities [Member] \| Corporate Debt Securities [Member]
Amortized Cost		10,054
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		$ 10,054

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

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=121645371&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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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

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