| Cover | Dec. 28, 2020 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 28, 2020 |
| Entity File Number | 001-38795 |
| Entity Registrant Name | RMG ACQUISITION CORP. |
| Entity Central Index Key | 0001757932 |
| Entity Tax Identification Number | 83-2289787 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 50 West Street |
| Entity Address, Address Line Two | Suite 40-C |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10006 |
| City Area Code | 212 |
| Local Phone Number | 785-2579 |
| Written Communications | true |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
| One Class Common Stock Member | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Units, each consisting of one share of Class A common stock and one redeemable warrant |
| Trading Symbol | RMG.UT |
| Security Exchange Name | NYSE |
| Class A Common stock | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Class A common stock, par value $0.0001 per share |
| Trading Symbol | RMG |
| Security Exchange Name | NYSE |
| Warrants To Purchase Class Common Stock Member | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Redeemable warrants, exercisable for shares of Class A common stock at an exercise price of $11.50 per share |
| Trading Symbol | RMG.WT |
| Security Exchange Name | NYSE |
