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Common Stock Warrants - Summary of Common Stock Warrants Outstanding (Details) - $ / shares | 6 Months Ended |
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Class Of Warrant Or Right [Line Items] |  |
Warrant outstanding (in shares) | 23,644 | 17,312
Five Year Warrants Issued in February 2015 [Member] | Stockholders' Equity [Member] |  |
Class Of Warrant Or Right [Line Items] |  |
Issuance Date | 2015-02 |
Expiration Date | 2020-02 |
Exercise price of warrants (in dollars per share) | $ 66.20 |
Warrant outstanding (in shares) | 9,063 | 9,063
Five Year Warrants Issued in February 2016 [Member] | Stockholders' Equity [Member] |  |
Class Of Warrant Or Right [Line Items] |  |
Issuance Date | 2016-02 |
Expiration Date | 2021-02 |
Exercise price of warrants (in dollars per share) | $ 15.40 |
Warrant outstanding (in shares) | 8,249 | 8,249
Five Year Warrants Issued in May 2018 [Member] | Stockholders' Equity [Member] |  |
Class Of Warrant Or Right [Line Items] |  |
Issuance Date | 2018-05 |
Expiration Date | 2028-05 |
Exercise price of warrants (in dollars per share) | $ 23.69 |
Warrant outstanding (in shares) | 6,332 |

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- Definition Exercise price per share or per unit of warrants or rights outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(4)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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