Entity Wide Disclosures - Segment Data for our Three Operating Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 280,859	$ 240,619	$ 503,553	$ 428,740
Operating income	19,399	28,674	23,848	40,499
Capital expenditures	10,579	5,957	21,797	11,425
Depreciation and amortization	8,658	5,635	16,542	11,164
Operating Segments [Member] | IHT Segment [Member]
Segment Reporting Information [Line Items]
Revenues	174,694	134,080	311,461	239,674
Operating income	19,758	21,999	32,285	34,286
Capital expenditures	2,430	2,325	5,763	3,864
Depreciation and amortization	4,872	2,068	8,904	4,069
Operating Segments [Member] | MS Segment [Member]
Segment Reporting Information [Line Items]
Revenues	86,390	84,221	154,748	152,067
Operating income	9,830	8,809	13,461	15,513
Capital expenditures	2,119	907	4,558	2,087
Depreciation and amortization	1,969	1,884	4,094	3,748
Operating Segments [Member] | Quest Integrity [Member]
Segment Reporting Information [Line Items]
Revenues	19,775	22,318	37,344	36,999
Operating income	3,591	6,350	5,336	7,117
Capital expenditures	456	815	1,694	1,611
Depreciation and amortization	1,525	1,420	2,966	2,825
Corporate and shared support services [Member]
Segment Reporting Information [Line Items]
Operating income	(13,780)	(8,484)	(27,234)	(16,417)
Capital expenditures	5,574	1,910	9,782	3,863
Depreciation and amortization	$ 292	$ 263	$ 578	$ 522