Fair Value of Warrants - Summary of Derivative Warrant Activity (Details) $ in Thousands |
6 Months Ended |
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Jun. 30, 2019
USD ($)
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| Class of Warrants Outstanding [Roll Forward] | |
| Fair value of warrants outstanding as of December 31, 2018 | $ 248 |
| Change in fair value of warrants | (199) |
| Fair value of warrants outstanding as of June 30, 2019 | 49 |
| 2016 Offerings | |
| Class of Warrants Outstanding [Roll Forward] | |
| Fair value of warrants outstanding as of December 31, 2018 | 225 |
| Change in fair value of warrants | (176) |
| Fair value of warrants outstanding as of June 30, 2019 | 49 |
| 2017 Offering | |
| Class of Warrants Outstanding [Roll Forward] | |
| Fair value of warrants outstanding as of December 31, 2018 | 23 |
| Change in fair value of warrants | (23) |
| Fair value of warrants outstanding as of June 30, 2019 | $ 0 |
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- Definition Change In Fair Value Of Warrant Liability No definition available.
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- Definition Class of Warrants Outstanding [Roll Forward] No definition available.
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- Definition Value of outstanding derivative securities that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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