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Loan Agreements - Fair Value of Preferred Stock Warrants Calculated using Black-Scholes Assumptions (Detail) (Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member], Series D Convertible Preferred Stock [Member])	1 Months Ended
	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Loan and Security Agreement with Lighthouse Capital Partners VI, L.P. [Member] | Series D Convertible Preferred Stock [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Contractual life	9 years 3 months 15 days	9 years 8 months 9 days	10 years
Expected volatility	80.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_LongtermDebtTypeAxis = us-gaap_LoansPayableMember / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember	80.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_LongtermDebtTypeAxis = us-gaap_LoansPayableMember / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember	80.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_LongtermDebtTypeAxis = us-gaap_LoansPayableMember / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember
Risk-free interest rate	1.68%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_LoansPayableMember / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember	2.17%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_LoansPayableMember / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember	1.98%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_LongtermDebtTypeAxis = us-gaap_LoansPayableMember / us-gaap_StatementClassOfStockAxis = us-gaap_SeriesDPreferredStockMember

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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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

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

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

+ 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

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