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Stockholders' Equity - Common stock (Details) - USD ($) |  |  |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 02, 2020 | Sep. 30, 2020 | Jun. 16, 2020 | Sep. 21, 2018 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Sep. 30, 2019 | Dec. 31, 2019 | Mar. 16, 2020
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Sale of common stock, net |  |  |  |  | $ 64,000 | $ 1,873,000 |  |  |  |
Proceeds from sale of common stock, net |  |  |  |  |  |  |  | $ 15,964,000 |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  | 5,000,000 | 139,855,000 |  |  |  |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Sale of common stock, net |  |  |  | $ 5,000,000 |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  | 32,170 |
Proceeds from sale of common stock, net |  |  |  |  |  |  |  |  | $ 300,000 |
Period exercisable from the date of issuance |  |  |  | 24 months |  |  |  |  |  |
Remaining availability under financing facility |  | $ 0 |  |  |  |  |  |  |  |
Common Stock [Member] | Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  | 12,802 |  |  |
Proceeds from sale of common stock, net |  |  |  |  |  |  | $ 300,000 |  |  |
Common Stock [Member] | 2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Sale of common stock, net |  | $ 25,000,000 |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 0 |  |  |  |  |  |  |  |
Period exercisable from the date of issuance |  | 36 months |  |  |  |  |  |  |  |
Closing price per share |  |  |  |  |  |  |  |  |  | $ 1.05
Common Stock [Member] | 2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | 180,701 |  |  |  |  |  |  |  |  |
Fair value of commitment fee | $ 500,000 |  |  |  |  |  |  |  |  |
Common Stock [Member] | 2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Minimum [Member] | Single Regular Purchase [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Sale of common stock, net |  | $ 500,000 |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 50,000 |  |  |  |  |  |  |  |
Common Stock [Member] | 2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  | 23,800,000 |  |  |  |  |  |  |
Percentage issuance of common stock |  |  | 19.99% |  |  |  |  |  |  |
Common Stock [Member] | 2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Maximum [Member] | Single Regular Purchase [Member] |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 100,000 |  |  |  |  |  |  |  |
Closing price per share |  | $ 0.25 |  |  |  |  |  |  |  |

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