Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended	7 Months Ended	12 Months Ended
	Jul. 31, 2015	Jun. 30, 2015	Aug. 31, 2014	Jul. 31, 2013	Aug. 31, 2015	Dec. 31, 2015	May. 31, 2015	May. 31, 2014	May. 31, 2013	Jul. 07, 2015	Nov. 30, 2010
Business Acquisition [Line Items]
Ownership percentage acquired						50.00%
Business acquisition, contingent consideration	$ 10,000
Intangible assets						$ 99,119	$ 20,268	$ 23,513
Business acquisition, goodwill						256,654	107,773	113,763	$ 103,466
Business acquisition total consideration, net of cash acquired						262,100	3,075	10,175	18,589
Number of shares estimated to be issued to acquire non-controlling interests					728,266
Cash payment to acquire non controlling interest					$ 5,900
IHT Segment [Member]
Business Acquisition [Line Items]
Business acquisition, goodwill						207,497	60,737	63,249	$ 53,800
Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets						90,293	13,501	15,685
Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Intangible assets						1,430	54	237
Trade Names [Member]
Business Acquisition [Line Items]
Intangible assets						4,359	$ 3,327	$ 3,608
Mechanical Service [Member]
Business Acquisition [Line Items]
Business acquisition, purchase price		$ 12,300
Business acquisition, contingent consideration		1,800
Business acquisition, goodwill		2,500
Business acquisitions, cash acquired		100
Business acquisition, net working capital		3,000
Business acquisition, fixed assets		600
Business acquisition, allocated to goodwill and intangible assets		$ 8,800
Business acquisition, contingent consideration thresholds period		3 years
Business acquisition, Contingent consideration based upon achievement of operating earnings thresholds		$ 4,000
Mechanical Service [Member] | United Kingdom [Member]
Business Acquisition [Line Items]
Business acquisition, contingent consideration			$ 300
Business acquisitions, cash acquired			200
Business acquisition total consideration, net of cash acquired			$ 3,100
Global Ascent, Inc.
Business Acquisition [Line Items]
Business acquisition, purchase price				$ 12,900
Business acquisition, contingent consideration				1,900
Business acquisition, expected deductible goodwill recognized for tax purposes				9,200
Business acquisition, net working capital				1,300
Business acquisition, allocated to goodwill and intangible assets				$ 11,600
Business acquisition, contingent consideration thresholds period				6 years
Business acquisition, Contingent consideration based upon achievement of operating earnings thresholds				$ 4,000
Quest Integrity [Member]
Business Acquisition [Line Items]
Purchase percentage of quest											95.00%
Qualspec Group [Member]
Business Acquisition [Line Items]
Ownership percentage acquired	100.00%
Business acquisition, purchase price	$ 255,500
Increase in revenue due to acquisition	170,000
Business acquisition, contingent consideration fair value	5,800					0
Intangible assets	78,100
Business acquisition, goodwill										$ 148,482
Business acquisition, expected deductible goodwill recognized for tax purposes	109,600
Fair value of accounts receivables acquired	21,500
Gross contractual amount	22,500
Uncollectible amount	1,000
Acquisition related costs recognized in selling, general and administrative expenses						$ 3,600
Business acquisition, fixed assets										$ 15,472
Qualspec Group [Member] | IHT Segment [Member]
Business Acquisition [Line Items]
Business acquisition, goodwill	148,500
Qualspec Group [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets	$ 75,200
Acquired intangible asset useful life	15 years
Qualspec Group [Member] | Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Intangible assets	$ 1,600
Acquired intangible asset useful life	5 years
Qualspec Group [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Intangible assets	$ 1,300
Acquired intangible asset useful life	1 year