Fair Value Measurements - Schedule of Remeasured Preferred Stock Warrants to Fair Value using OPM and/or PWERM Models (Detail) - Outstanding Preferred Stock Warrants [Member]	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Minimum [Member]
Class of Stock [Line Items]
Expected term (in years)	1 year 2 months 12 days	2 years 6 months
Expected volatility	69.00%	66.00%
Risk-free interest rate	0.30%	0.40%
Expected dividend rate	0.00%	0.00%
Discount for lack of marketability	19.50%	23.70%
Maximum [Member]
Class of Stock [Line Items]
Expected term (in years)	2 years 6 months	3 years 1 month 6 days
Expected volatility	86.00%	70.00%
Risk-free interest rate	0.60%	0.70%
Expected dividend rate	0.00%	0.00%
Discount for lack of marketability	24.30%	25.80%

Fair value assumptions discount for lack of marketability.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

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).

+ References

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

+ Details

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- Definition

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.

+ References

+ Details

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- Definition

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

+ References

+ Details

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- Definition

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

+ References

+ Details

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