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SUBSEQUENT EVENTS - Additional Information (Detail) - Biogen MA, Inc. - USD ($) $ in Millions | 1 Months Ended
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Apr. 30, 2020 | Apr. 30, 2020 | Feb. 29, 2020
Collaboration And License Agreement |  |  |
Subsequent Event [Line Items] |  |  |
Proceeds from collaborators |  |  | $ 125.0
Subsequent Event | Stock Purchase Agreement |  |  |
Subsequent Event [Line Items] |  |  |
Consideration received on transaction | $ 225.0 | $ 225.0 |
Number of shares issued in transaction (in shares) | 24,420,157 |  |
Subsequent Event | Collaboration And License Agreement |  |  |
Subsequent Event [Line Items] |  |  |
Proceeds from collaborators |  | $ 125.0 |

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