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RELATED PARTY TRANSACTIONS, Administrative Support Agreement (Q1) (Details) - Sponsor [Member] - Administrative Support Agreement [Member] - USD ($) |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Sep. 14, 2020 | Mar. 31, 2021 | Dec. 31, 2020
Related Party Transactions [Abstract] |  |  |
Related party expense |  | $ 30,000 | $ 40,000
Maximum [Member] |  |  |
Related Party Transactions [Abstract] |  |  |
Related party transaction | $ 10,000 |  |

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