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Document And Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Mar. 04, 2022
Jun. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2021    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Trading Symbol SMHI    
Entity Registrant Name SEACOR Marine Holdings Inc.    
Entity Central Index Key 0001690334    
Current Fiscal Year End Date --12-31    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company true    
ICFR Auditor Attestation Flag false    
Entity Ex Transition Period true    
Entity Shell Company false    
Title of 12(b) Security Common stock    
Security Exchange Name NYSE    
Entity File Number 1-37966    
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    
Document Annual Report true    
Document Transition Report false    
Entity Common Stock, Shares Outstanding   25,992,237  
Entity Public Float     $ 96.2
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Auditor Firm ID 248    
Auditor Name GRANT THORNTON LLP    
Auditor Location Houston, Texas    
Documents Incorporated by Reference

Portions of the Registrant’s definitive proxy statement for its 2022 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission (the "SEC") pursuant to Regulation 14A within 120 days after the end of the Registrant’s last fiscal year is incorporated by reference into Part III of this Annual Report on Form 10-K.