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Stockholders' Equity - Common stock (Details) - USD ($) |  |  |  | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Oct. 23, 2020 | Sep. 30, 2020 | Jun. 16, 2020 | Jun. 30, 2021 | Mar. 31, 2021 | Jun. 30, 2021 | Jun. 30, 2020 | Sep. 30, 2020 | Dec. 31, 2020
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Sale of common stock, net |  |  |  | $ 5,094,000 | $ 7,078,000 |  |  |  |
Proceeds from sale of common stock, net |  |  |  |  |  | $ 12,291,000 | $ 0 |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Sale of common stock, net |  |  |  | $ 2,000 | $ 2,000 |  |  |  |
Common stock issued (in shares) |  |  |  | 1,907,000,000 | 2,534,879,000 |  |  |  |
Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Sale of common stock, net |  |  |  |  |  |  |  | $ 25,000,000.0 |
Period exercisable from the date of issuance |  |  |  |  |  |  |  | 36 months |
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Sale of common stock, net |  | $ 25,000,000.0 |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  | 2,262,686 |  |  | 353,113
Period exercisable from the date of issuance |  | 36 months |  |  |  |  |  |  |
Closing price per share |  |  | $ 1.05 |  |  |  |  |  |
Proceeds from sale of common stock, net |  |  |  |  |  | $ 6,000,000.0 |  |  | $ 700,000
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] | Commitment Fee |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  | 180,701
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Percentage issuance of common stock |  |  | 19.99% |  |  |  |  |  |
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [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 |  |  |  |  |  |  |
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  | 23,800,000 |  |  |  |  |  |
Lincoln Park Capital Fund, LLC [Member] | 2020 Repurchase Agreement [Member] | Common Stock [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 |  |  |  |  |  | $ 0.25 |
Canaccord Genuity LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  | 2,179,193 |  |  | 1,616,331
Proceeds from sale of common stock, net | $ 10,000,000 |  |  |  |  | $ 6,300,000 |  |  | $ 3,200,000
Remaining availability under financing facility | 0 |  |  |  |  |  |  |  |
Canaccord Genuity LLC [Member] | Sales Agreement | Common Stock [Member] | At The Market Offering Program |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Remaining availability under financing facility | $ 0 |  |  |  |  |  |  |  |
Canaccord Genuity LLC [Member] | Distribution Agreement [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |
Remaining availability under financing facility |  |  |  | $ 0 |  | $ 0 |  |  |

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