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Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | 12 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Mar. 31, 2014
Warrant Liabilities [Member]
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Mar. 31, 2013
Warrant Liabilities [Member]
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Mar. 31, 2014
Warrant Liabilities [Member]
Minimum [Member]
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Dec. 31, 2013
Warrant Liabilities [Member]
Minimum [Member]
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Mar. 31, 2014
Warrant Liabilities [Member]
Maximum [Member]
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Dec. 31, 2013
Warrant Liabilities [Member]
Maximum [Member]
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Mar. 31, 2014
Recurring [Member]
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Dec. 31, 2013
Recurring [Member]
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Mar. 31, 2014
Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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Dec. 31, 2013
Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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Mar. 31, 2014
Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
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Dec. 31, 2013
Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
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Mar. 31, 2014
Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
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Dec. 31, 2013
Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
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| Assets: | ||||||||||||||||||||||||
| Money market funds | $ 63,561 | [1] | $ 82,759 | [1] | $ 63,561 | [1] | $ 82,759 | [1] | $ 0 | [1] | $ 0 | [1] | $ 0 | [1] | $ 0 | [1] | ||||||||
| U.S. treasury securities | 19,996 | 19,990 | 19,996 | 19,990 | 0 | 0 | 0 | 0 | ||||||||||||||||
| Foreign exchange options | 239 | 361 | 0 | 0 | 239 | 361 | 0 | 0 | ||||||||||||||||
| Total | 83,796 | 103,110 | 83,557 | 102,749 | 239 | 361 | 0 | 0 | ||||||||||||||||
| Liabilities: | ||||||||||||||||||||||||
| Contingent warrant liabilities | 47,342 | 69,869 | 0 | 0 | 0 | 0 | 47,342 | 69,869 | ||||||||||||||||
| Fair Value Inputs, Liabilities, Quantitative Information [Line Items] | ||||||||||||||||||||||||
| Expected volatility (in hundredths) | 74.20% | 66.10% | 88.40% | 86.60% | ||||||||||||||||||||
| Risk-free interest rate (in hundredths) | 0.10% | 0.10% | 0.90% | 0.80% | ||||||||||||||||||||
| Expected term | 0 years 8 months 12 days | 0 years 10 months 24 days | 2 years 10 months 24 days | 3 years 2 months 12 days | ||||||||||||||||||||
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | ||||||||||||||||||||||||
| Balance, beginning of period | 69,869 | |||||||||||||||||||||||
| Reclassification of contingent warrant liability to equity upon exercise of warrants | (2,525) | |||||||||||||||||||||||
| Net increase in fair value of contingent warrant liabilities upon revaluation | (20,002) | 12,800 | ||||||||||||||||||||||
| Balance, end of period | $ 47,342 | |||||||||||||||||||||||
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