Cover - shares	9 Months Ended
	Sep. 30, 2021	Oct. 28, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-34481
Entity Registrant Name	Mistras Group, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-3341267
Entity Address, Address Line One	195 Clarksville Road
Entity Address, City or Town	Princeton Junction,
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	08550
City Area Code	609
Local Phone Number	716-4000
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	MG
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		29,458,243
Entity Central Index Key	0001436126
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3