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Liquidity and Going Concern - Additional Information (Details) - USD ($) |  |  | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | ---
Oct. 23, 2020 | Sep. 30, 2020 | Jun. 30, 2021 | Mar. 31, 2021 | Jun. 30, 2020 | Mar. 31, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Sep. 30, 2020 | Dec. 31, 2020
Liquidity [Line Items] |  |  |  |  |  |  |  |  |  |
Net loss |  |  | $ (2,800,000) | $ (2,720,000) | $ (1,839,000) | $ (1,087,000) | $ (5,520,000) | $ (2,926,000) |  |
Accumulated deficit |  |  | (439,031,000) |  |  |  | (439,031,000) |  |  | $ (433,511,000)
Net cash used in operating activities |  |  |  |  |  |  | $ (5,405,000) | (2,911,000) |  |
Substantial doubt about going concern, description |  |  |  |  |  |  | These factors raise substantial doubt about the Company’s ability to continue as a going concern. |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  | $ 12,291,000 | $ 0 |  |
Sale of common stock, net |  |  | $ 5,094,000 | $ 7,078,000 |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Liquidity [Line Items] |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  | 1,907,000,000 | 2,534,879,000 |  |  |  |  |  |
Sale of common stock, net |  |  | $ 2,000 | $ 2,000 |  |  |  |  |  |
Underwriter [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Liquidity [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  | $ 6,300,000 |  |  | $ 3,200,000
Common stock issued (in shares) |  |  |  |  |  |  | 2,179,193 |  |  | 1,616,331
Remaining common stock issued and sold (in shares) |  |  | 0 |  |  |  | 0 |  |  |
Canaccord Genuity LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Liquidity [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock | $ 10,000,000 |  |  |  |  |  | $ 6,300,000 |  |  | $ 3,200,000
Remaining availability under financing facility | $ 0 |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  | 2,179,193 |  |  | 1,616,331
Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |
Liquidity [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] | Common Stock [Member] | 2020 Repurchase Agreement [Member] |  |  |  |  |  |  |  |  |  |
Liquidity [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  | $ 6,000,000.0 |  |  | $ 700,000
Common stock issued (in shares) |  |  |  |  |  |  | 2,262,686 |  |  | 353,113
Sale of common stock, net |  | $ 25,000,000.0 |  |  |  |  |  |  |  |
Period exercisable from the date of issuance |  | 36 months |  |  |  |  |  |  |  |
Common stock issued as commitment fee (in shares) |  |  |  |  |  |  |  |  |  | 180,701

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