Common and Preferred Stock Warrants - Assumptions Used in Valuing 2012 SVB Warrant (Detail) (2012 SVB Warrant [Member])	0 Months Ended	12 Months Ended
Feb. 06, 2014	Sep. 04, 2012	Dec. 31, 2013	Dec. 31, 2012
2012 SVB Warrant [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk-free interest rate	3.04%	1.67%	2.79%	1.74%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	8 years 6 months 29 days	10 years	8 years 8 months 5 days	9 years 4 months 6 days
Expected volatility	77.90%	76.92%	77.90%	74.00%

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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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