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Common Stock - Stock Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |  |  | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2019 | May 30, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jun. 19, 2018
Class Of Warrant Or Right [Line Items] |  |  |  |  |  |
Exercise price per unit of warrant |  |  |  |  |  | $ 4.00
Proceeds from aggregate warrant exercise |  |  | $ 4,199 | $ 1,324 |  |
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 |  |
Number of warrants exercised |  |  |  |  | 0 |
Common stock, shares issued |  |  | 29,485,178 | 6,721,117 |  |
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 | $ 1,300 |  |
Number of warrants exercised |  |  | 837,500 | 330,500 |  |
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 |  |  |  |
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 Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + 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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