Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 09, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 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, par value $.01 par value
Trading Symbol	MG
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 176.5
Entity Common Stock, Shares Outstanding		29,545,813
Documents Incorporated by Reference	Information required by Part III (Items 10, 11, 12, 13 and 14) is incorporated by reference to portions of the registrant’s definitive proxy statement for its 2022 annual meeting of shareholders (the “Proxy Statement”), which is expected to be filed not later than 120 days after the registrant’s fiscal year ended December 31, 2021. Except as expressly incorporated by reference, the Proxy Statement shall not be deemed to be a part of this report on Form 10-K.
Entity Central Index Key	0001436126
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY