Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 31, 2015	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2014	May 31, 2016	May 31, 2015	May 31, 2014
Basic earnings per share
Net income attributable to Mistras Group, Inc.	$ 2,764	$ 3,593	$ 11,425	$ 6,872	$ 2,171	$ 1,817	$ 10,427	$ 1,666	$ 24,654	$ 16,081	$ 22,518
Denominator
Weighted average common shares outstanding (in shares)									28,856	28,613	28,365
Basic earnings per share (in dollars per share)	$ 0.10	$ 0.12	$ 0.40	$ 0.24	$ 0.08	$ 0.06	$ 0.36	$ 0.06	$ 0.85	$ 0.56	$ 0.79
Denominator
Weighted average common shares outstanding (in shares)									28,856	28,613	28,365
Dilutive effect of stock options outstanding (in shares)									712	719	775
Dilutive effect of restricted stock units outstanding (in shares)									323	258	184
Weighted average common shares outstanding, diluted (in shares)									29,891	29,590	29,324
Diluted earnings per share (in dollars per share)	$ 0.09	$ 0.12	$ 0.39	$ 0.23	$ 0.07	$ 0.06	$ 0.35	$ 0.06	$ 0.82	$ 0.54	$ 0.77
Earnings per share
Total shares									29	7	126
Potential common stock attributable to stock options outstanding
Earnings per share
Total shares									5	6	5
Potential common stock attributable to performance awards outstanding
Earnings per share
Total shares									24	1	121