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Common Stock - Common Stock Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands |  | 6 Months Ended |
--- | --- | --- | ---
May 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Class of Warrant or Right [Line Items] |  |  |  |
Common stock, par value |  | $ 0.001 |  | $ 0.001
Proceeds from exercise of warrants, net of issuance costs | $ 4,200 | $ 589 | $ 4,199 |
Expected volatility |  | 104.64% | 94.25% |
Risk-free interest rate |  | 1.43% | 2.52% |
Expected term |  | 5 years 11 months 23 days | 5 years 11 months 19 days |
October 2018 Financing [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Warrants to purchase common stock | 13,515 |  |  |
Common stock, par value | $ 0.001 |  |  |
Exercise price per unit of warrant | $ 62.89 |  |  |
June 2018 Financing [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Warrants to purchase common stock | 41,875 |  |  |
Exercise price per unit of warrant | $ 80.00 |  |  |
New Warrant [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Warrants to purchase common stock | 60,000 |  |  |
Exercise price per unit of warrant | $ 90.00 |  |  |
Warrants, exercise period | 6 years |  |  |
Fair value of warrants recognized into accumulated deficit |  | $ (3,900) |  |
Stock price |  | $ 84.60 |  |
Expected volatility |  | 97.16% |  |
Risk-free interest rate |  | 2.06% |  |
Expected term |  | 6 years |  |
Warrants Issued in December 2019 [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Warrants to purchase common stock |  | 89,281 |  |
Exercise price per unit of warrant |  | $ 6.6000 |  |
Proceeds from exercise of warrants, net of issuance costs |  | $ 600 |  |
Warrants Issued in June 2018 [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Warrants to purchase common stock |  |  | 41,875 |
Exercise price per unit of warrant |  | $ 80.0000 | $ 80.00 |
Proceeds from exercise of warrants, net of issuance costs |  |  | $ 3,400 |
Warrants Issued in October 2018 [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Warrants to purchase common stock |  |  | 13,515 |
Exercise price per unit of warrant |  | $ 62.8900 | $ 62.89 |
Proceeds from exercise of warrants, net of issuance costs |  |  | $ 800 |

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- Definition Exercise price per share or per unit of warrants or rights outstanding. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 + 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://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 + Details
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- Definition The cash inflow associated with the amount received from holders exercising their stock warrants. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585 + 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=120381028&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=120381028&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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- 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=117815213&loc=d3e19207-110258 + Details
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