Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Financial Liabilities (Details) - USD ($) $ in Thousands  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016  | 
Dec. 31, 2015  | 
Dec. 31, 2014  | 
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| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | |||
| Reclassification of contingent warrant liability to equity upon exercise of warrants | $ (3,552) | $ (2,526) | |
| Warrant Liabilities [Member] | |||
| Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | |||
| Beginning balance | $ 10,464 | 31,828 | |
| Reclassification of contingent warrant liability to equity upon exercise of warrants | (3,552) | ||
| Decrease in estimated fair value of contingent warrant liabilities upon revaluation | $ (10,464) | (17,812) | |
| Ending balance | $ 10,464 | $ 31,828 | |
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Amount of increase (decrease) of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Noncash value related to the reclassification of a contingent warrant liability to equity upon exercise of warrants during the reporting period No definition available. 
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- Details 
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