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Common Stock - Common Stock Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |  | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
May 30, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018 | Jun. 19, 2018 | May 23, 2018
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Common stock, par value |  | $ 0.001 |  | $ 0.001 |  | $ 0.001
Exercise price per unit of warrant |  |  |  |  | $ 4.00 |
Proceeds from aggregate warrant exercise |  | $ 4,199 | $ 1,274 |  |  |
Expected volatility |  | 94.25% | 88.23% |  |  |
Risk-free interest rate |  | 2.52% | 2.93% |  |  |
Expected term |  | 5 years 11 months 19 days | 5 years 8 months 4 days |  |  |
New Warrant [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Fair value of warrants recognized into accumulated deficit |  | $ (3,900) |  |  |  |
Stock price |  | $ 4.23 |  |  |  |
Expected volatility |  | 97.16% |  |  |  |
Risk-free interest rate |  | 2.06% |  |  |  |
Expected term |  | 6 years |  |  |  |
Warrants Issued In June 2018 [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Exercise price per unit of warrant |  | $ 4.0000 | $ 4.00 |  |  |
Proceeds from aggregate warrant exercise |  | $ 3,400 | $ 500 |  |  |
Number of warrants exercised |  | 837,500 | 130,500 |  |  |
Warrants Issued in October 2018 [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Exercise price per unit of warrant |  | $ 3.1445 |  |  |  |
Proceeds from aggregate warrant exercise |  | $ 800 |  |  |  |
Number of warrants exercised |  | 270,313 |  |  |  |
Armistice [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Proceeds from aggregate warrant exercise | $ 4,200 |  |  |  |  |
Armistice [Member] | October 2018 Financing [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Warrants to purchase common stock | 270,313 |  |  |  |  |
Common stock, par value | $ 0.001 |  |  |  |  |
Exercise price per unit of warrant | $ 3.1445 |  |  |  |  |
Armistice [Member] | June 2018 Financing [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Warrants to purchase common stock | 837,500 |  |  |  |  |
Exercise price per unit of warrant | $ 4.00 |  |  |  |  |
Armistice [Member] | New Warrant [Member] |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |
Warrants to purchase common stock | 1,200,000 |  |  |  |  |
Exercise price per unit of warrant | $ 4.50 |  |  |  |  |
Warrants, exercise period | 6 years |  |  |  |  |

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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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- Definition Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares. + 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)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
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