Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	SMHI
Entity Registrant Name	SEACOR Marine Holdings Inc.
Entity Central Index Key	0001690334
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		24,194,383
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	1-37966
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
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock
Security Exchange Name	NYSE
Document Quarterly Report	true
Document Transition Report	false