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Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Nov. 27, 2019 | Jun. 30, 2021 | May 31, 2020 | Oct. 31, 2019 | Dec. 31, 2018 | Aug. 31, 2018 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020 | Aug. 06, 2018
Stock transactions |  |  |  |  |  |  |  |  |  |
Proceeds from public offering of common stock, net of issuance costs |  |  |  |  |  |  | $ 123,995 | $ 105,478 |  |
Par value (per share) |  |  |  |  |  |  | $ 0.00001 |  | $ 0.00001 |
2019 Form S-3 |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Common stock available for sale |  |  |  |  |  |  | $ 94,200 |  |  |
Maximum aggregate offering price |  |  |  | $ 250,000 |  |  |  |  |  |
2019 Sales Agreement |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Common stock available for sale |  |  |  |  |  |  | $ 31,900 |  |  |
Maximum aggregate offering price | $ 250,000 |  |  | $ 75,000 |  |  |  |  |  |
Underwritten public offering |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Net proceeds from sale of common stock |  | $ 123,800 | $ 105,300 |  |  |  |  |  |  |
Common stock issued (in shares) |  | 3,046,358 | 7,000,000 |  |  |  |  |  |  |
Common stock issued, price per share |  | $ 37.75 | $ 14.00 |  |  |  |  |  |  |
underwritten public offering, Additional offering |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  | 456,953 | 1,050,000 |  |  |  |  |  |  |
Common stock issued, price per share |  | $ 37.75 | $ 14.00 |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  | 3,503,311 | 8,050,000 | 4,761,904 |
Common stock issued, price per share |  |  |  |  |  |  |  |  | $ 21.00 |
Proceeds from public offering of common stock, net of issuance costs |  |  |  |  |  |  |  |  | $ 107,600 |
Common Stock | Private Placement |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Number of warrants exercised |  |  |  |  |  |  | 0 |  |  |
Common Stock | underwritten public offering, Additional offering |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  | 714,285 |
Common stock issued, price per share |  |  |  |  |  |  |  |  | $ 21.00 |
Investors | Private Placement |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Aggregate shares of common stock sold |  |  |  |  |  | 2,750,000 |  |  |  |
Common stock sold, price per share |  |  |  |  |  | $ 8.00 |  |  |  |
Net proceeds from sale of common stock |  |  |  |  |  | $ 21,700 |  |  |  |
Warrants issued to purchase common stock, number of shares |  |  |  |  |  |  |  |  |  | 2,750,000
Warrants exercisable date |  |  |  |  |  | Aug. 08, 2023 |  |  |  |
Exchange Agreement | Exchanging Stockholders |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Warrants issued to purchase common stock, number of shares |  |  |  |  | 1,000,000 |  |  |  |  |
Exercise Price (per share) |  |  |  |  | $ 0.00001 |  |  |  |  |
Common stock exchanged for pre-funded warrants |  |  |  |  | 1,000,000 |  |  |  |  |
Par value (per share) |  |  |  |  | $ 0.00001 |  |  |  |  |
Duration of warrants from date of issuance (in years) |  |  |  |  | 10 years |  |  |  |  |
Equity method investment, ownership percentage |  |  |  |  | 9.99% |  |  |  |  |
Exchange Agreement | Exchanging Stockholders | Common Stock |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Remaining number of Exchange Warrants unexercised |  |  |  |  |  |  | 400,000 |  |  |
$10.00 per share | Investors | Private Placement |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Warrants to purchase common stock (in shares) |  |  |  |  |  |  |  |  |  | 1,375,000
Exercise Price (per share) |  |  |  |  |  |  |  |  |  | $ 10.00
$15.00 per share | Investors | Private Placement |  |  |  |  |  |  |  |  |  |
Stock transactions |  |  |  |  |  |  |  |  |  |
Warrants to purchase common stock (in shares) |  |  |  |  |  |  |  |  |  | 1,375,000
Exercise Price (per share) |  |  |  |  |  |  |  |  |  | $ 15.00

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