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Preferred and Common Stock Warrants - Assumptions Used to Calculate Fair Value of Outstanding Warrants (Details) - Redeemable Convertible Preferred Stock Warrants | Dec. 31, 2017 | Dec. 31, 2016
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Dividend Yield |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input | 0 | 0
Expected Term |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input | 2 years 9 months |
Expected Term | Minimum |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input |  | 6 months
Expected Term | Maximum |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input |  | 3 years 9 months
Risk-Free Interest Rates |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input | 0.018 |
Risk-Free Interest Rates | Minimum |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input |  | 0.010
Risk-Free Interest Rates | Maximum |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input |  | 0.016
Expected Volatility |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input | 0.346 |
Expected Volatility | Minimum |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input |  | 0.348
Expected Volatility | Maximum |  |
Class of Warrant or Right [Line Items] |  |
Outstanding warrants measurement input |  | 0.392

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- Definition Value of input used to measure outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- Definition Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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