Segment Data for our Three Operating Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Nov. 30, 2014	Nov. 30, 2013	Nov. 30, 2014	Nov. 30, 2013
Segment Reporting Information [Line Items]
Revenues	$ 240,619us-gaap_SalesRevenueNet	$ 200,493us-gaap_SalesRevenueNet	$ 428,740us-gaap_SalesRevenueNet	$ 374,804us-gaap_SalesRevenueNet
Operating income	28,674us-gaap_OperatingIncomeLoss	23,881us-gaap_OperatingIncomeLoss	40,499us-gaap_OperatingIncomeLoss	31,986us-gaap_OperatingIncomeLoss
Capital expenditures	5,957	7,396	11,425	13,619
Depreciation and amortization	5,635	5,308	11,164	10,691
Operating Segments \| IHT Segment
Segment Reporting Information [Line Items]
Revenues	134,080	109,427	239,674	205,260
Operating income	21,999	17,700	34,286	27,883
Capital expenditures	2,325	1,570	3,864	3,415
Depreciation and amortization	2,068	1,929	4,069	4,011
Operating Segments \| MS Segment
Segment Reporting Information [Line Items]
Revenues	84,221	70,987	152,067	136,756
Operating income	8,809	7,380	15,513	14,181
Capital expenditures	907	1,751	2,087	3,191
Depreciation and amortization	1,884	1,812	3,748	3,590
Operating Segments \| Quest Integrity
Segment Reporting Information [Line Items]
Revenues	22,318	20,079	36,999	32,788
Operating income	6,350	5,512	7,117	4,816
Capital expenditures	815	719	1,611	2,675
Depreciation and amortization	1,420	1,365	2,825	2,690
Corporate and shared support services
Segment Reporting Information [Line Items]
Operating income	(8,484)	(6,711)	(16,417)	(14,894)
Capital expenditures	1,910	3,356	3,863	4,338
Depreciation and amortization	$ 263	$ 202	$ 522	$ 400

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

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- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585

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- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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