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v3.20.1

Stockholders' Equity - Common stock (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 21, 2018 | Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2019
Class Of Stock [Line Items] |  |  |  |  |
Sale of common stock, net |  |  | $ 1,873,000 |  |
Proceeds from sale of common stock, net |  | $ 0 | $ 1,919,000 |  |
Common Stock [Member] |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |
Common stock issued (in shares) |  |  | 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 |

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