| Document and Entity Information | Nov. 04, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 4, 2021 |
| Entity Registrant Name | SEACOR Marine Holdings Inc. |
| Entity Central Index Key | 0001690334 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Entity File Number | 001-37966 |
| Entity Incorporation State or Country Code | DE |
| Entity Tax Identification Number | 47-2564547 |
| Entity Address, Address Line One | 12121 Wickchester Lane |
| Entity Address, Address Line Two | Suite 500 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77079 |
| City Area Code | (346) |
| Local Phone Number | 980-1700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Security12b Title | Common stock, par value $0.01 per share |
| Trading Symbol | SMHI |
| Security Exchange Name | NYSE |
