Fair Value Measurements - Fair Value of Outstanding Preferred Stock Warrants (Detail)	1 Months Ended	9 Months Ended	12 Months Ended
Jan. 31, 2013	Jul. 31, 2012	Sep. 30, 2013	Dec. 31, 2012 Preferred stock warrant liability [Member]	Dec. 31, 2012 Preferred stock warrant liability [Member] Minimum [Member]	Dec. 31, 2012 Preferred stock warrant liability [Member] Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Assumed risk-free interest rate	1.86%	1.43%	1.44%		0.25%	1.78%
Assumed volatility	80.00%	80.00%	71.00%	80.00%
Expected warrant life	9 years 6 months	10 years	5 years		2 years 29 days	9 years 6 months
Expected dividend yield	0.00%	0.00%	0.00%	0.00%

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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=25499696&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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