Note 9 - Redeemable Convertible Preferred Stock (Details) - Assumptions Used to Estimate Fair Value of Tranche Rights	12 Months Ended
Dec. 31, 2014
Upon Issuance [Member] \| Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected term (in years)	1 year 306 days
Expected volatility	63.00%
Risk-free interest rate	0.44%
Upon Issuance [Member] \| Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected term (in years)	3 years 6 months
Expected volatility	86.00%
Risk-free interest rate	1.12%
Upon Issuance [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected dividend yield	0.00%
Immediately Before IPO [Member] \| Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected volatility	63.00%
Risk-free interest rate	0.35%
Immediately Before IPO [Member] \| Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected volatility	71.00%
Risk-free interest rate	1.05%
Immediately Before IPO [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Expected term (in years)	8 hours 45 minutes 36 seconds
Expected dividend yield	0.00%

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

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Risk-free interest rate assumption used in valuing an instrument.

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