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Stockholders' Equity (Tables) | 9 Months Ended
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Sep. 30, 2019
Schedule of Estimated Fair Value Determined Using Option Pricing Model Assumptions | The warrants are not traded in an active securities market, and as such the estimated the fair value as of
|  | As of September 30, 2019 |  |  |  | As of December 31, 2018 |
Expected term |  | 1.6 years |  |  |  | 2.1 years |
Common stock market price |  | $ | 3.42 |  |  | $ | 14.50 |
Risk-free interest rate |  |  | 1.70 | % |  |  | 2.48 | %
Expected volatility |  |  | 176 | % |  |  | 125 | %
Resulting fair value (per 50 warrants as of September 30, 2019) |  | $ | 2.53 |  |  | $ | 0.13 |
Summary of Change in Level 3 Series T and Series U Warrant Liability Value | The following table summarizes the change in our Level 3 Series T and Series U warrants liabilities carrying value (in thousands):
Warrant liability |  |  | September 30, 2019 |  |  |  | December 31, 2018 |
Beginning balance |  | $ | 916 |  |  | $ | 3,148 |
Issuance |  |  | 10,215 |  |  |  | — |
Exercises/Settlement |  |  | (794) |  |  |  | — |
Change in fair value |  |  | 69 |  |  |  | (2,233) |
Ending balance |  | $ | 10,406 |  |  | $ | 916 |
Series U Warrants [Member] |
Schedule of Estimated Fair Value Determined Using Option Pricing Model Assumptions | The Series U warrants will be marked to market as of each balance sheet date until they are exercised or upon expiration, with the changes in fair value recorded as non-operating income or loss in the statement of operations and comprehensive income (loss).
|  | As of September 25, 2019 |  |  |  | As of September 30, 2019 |
Expected term |  | 5 years |  |  |  | 5 years |
Common stock market price |  | $ | 3.42 |  |  | $ | 3.42 |
Risk-free interest rate |  |  | 1.60 | % |  |  | 1.55 | %
Expected volatility |  |  | 134.9 | % |  |  | 134.9 | %
Resulting fair value (per warrant) |  | $ | 2.90 |  |  | $ | 2.90 |

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- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique used to measure similar asset in prior period by class of asset or liability on non-recurring basis. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Tabular disclosure of the fair value measurement of liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets), and gains or losses recognized in other comprehensive income (loss) and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs) by class of liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19279-110258 + Details
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