Fair value of financial instruments and investments (Details 4) (USD $) In Thousands, except Per Share data, unless otherwise specified
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12 Months Ended |
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Dec. 31, 2014
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Dec. 31, 2013
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Jun. 30, 2013
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Common stock |
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Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model |
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Fair value of shares (in dollars per share) |
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$ 15.00us-gaap_SharePrice / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember |
Warrant |
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Changes in the fair value of warrant liability |
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Beginning balance |
$ 58us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember |
$ 96us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember |
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Change in fair value of warrant liability |
130us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember |
(38)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember |
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Ending balance |
$ 188us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember |
$ 58us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember |
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Warrant | Minimum |
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Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model |
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Volatility (as a percent) |
68.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
61.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
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Risk-free interest rate (as a percent) |
0.89%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
0.07%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
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Strike price (in dollars per share) |
$ 128.00us-gaap_FairValueAssumptionsExercisePrice / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
$ 128.00us-gaap_FairValueAssumptionsExercisePrice / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MinimumMember |
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Expected life |
2 years 6 months |
3 months 18 days |
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Warrant | Maximum |
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Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model |
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Volatility (as a percent) |
70.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
89.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
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Risk-free interest rate (as a percent) |
1.65%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
2.10%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
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Strike price (in dollars per share) |
$ 2,520.00us-gaap_FairValueAssumptionsExercisePrice / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
$ 2,520.00us-gaap_FairValueAssumptionsExercisePrice / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
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Expected life |
4 years 8 months 12 days |
5 years 8 months 12 days |
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Warrant | Common stock |
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Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option-pricing model |
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Fair value of shares (in dollars per share) |
$ 51.77us-gaap_SharePrice / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember |
$ 16.97us-gaap_SharePrice / us-gaap_FairValueByLiabilityClassAxis = us-gaap_WarrantMember / us-gaap_StatementClassOfStockAxis = us-gaap_CommonStockMember |
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