SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Income Taxes (Q1) (Details) - USD ($) |
3 Months Ended | 12 Months Ended | |
|---|---|---|---|
Mar. 31, 2021 |
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES [Abstract] | |||
| Unrecognized tax benefits | $ 0 | $ 0 | $ 0 |
| Accrued interest and penalties | $ 0 | $ 0 |