Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Basic earnings per share
Net income attributable to Mistras Group, Inc.	$ 11,425	$ 10,427	$ 18,297	$ 12,093
Denominator:
Weighted average common shares outstanding (in shares)	28,869	28,619	28,796	28,547
Basic earnings per share (in dollars per share)	$ 0.40	$ 0.36	$ 0.64	$ 0.42
Denominator:
Weighted average common shares outstanding (in shares)	28,869	28,619	28,796	28,547
Dilutive effect of stock options outstanding (in shares)	592	675	610	763
Dilutive effect of restricted stock units outstanding (in shares)	133	103	235	241
Weighted average common shares outstanding, diluted (in shares)	29,594	29,397	29,641	29,551
Diluted earnings per share (in dollars per share)	$ 0.39	$ 0.35	$ 0.62	$ 0.41