Unaudited Condensed Consolidated Statements of Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 192,192	$ 182,169	$ 569,595	$ 561,592
Cost of revenue	129,241	124,260	386,721	389,131
Depreciation	5,182	5,577	16,160	16,902
Gross profit	57,769	52,332	166,714	155,559
Selling, general and administrative expenses	42,328	41,931	126,014	122,232
Bad debt provision for troubled customers, net of recoveries	0	0	2,798	0
Pension withdrawal expense (benefit)	(45)	5,886	489	5,886
Gain on sale of subsidiary	0	(2,384)	0	(2,384)
Research and engineering	650	745	2,261	2,414
Depreciation and amortization	4,089	2,920	12,380	8,834
Acquisition-related expense (benefit), net	(32)	217	970	(1,143)
Income from operations	10,779	3,017	21,802	19,720
Interest expense	2,959	1,894	10,065	5,581
Income before provision for income taxes	7,820	1,123	11,737	14,139
Provision for income taxes	4,733	2,133	6,493	6,229
Net income (loss)	3,087	(1,010)	5,244	7,910
Less: Net income (loss) attributable to non-controlling interests, net of taxes	(6)	1	13	13
Net income (loss) attributable to Mistras Group, Inc.	$ 3,093	$ (1,011)	$ 5,231	$ 7,897
Earnings (loss) per common share:
Basic (in dollars per share)	$ 0.11	$ (0.04)	$ 0.18	$ 0.28
Diluted (in dollars per share)	$ 0.11	$ (0.04)	$ 0.18	$ 0.27
Weighted-average common shares outstanding:
Basic (in shares)	28,800	28,429	28,678	28,360
Diluted (in shares)	29,156	28,429	29,022	29,447