Summary of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014
Goodwill [Line Items]
Balance at beginning of year	$ 113,763	$ 103,466
Acquisitions	103	10,386
Foreign currency adjustments	(6,093)	(89)
Balance at end of year	107,773	113,763
MS Segment
Goodwill [Line Items]
Balance at beginning of year	19,685	19,131
Acquisitions	103
Foreign currency adjustments	(2,322)	554
Balance at end of year	17,466	19,685
IHT Segment
Goodwill [Line Items]
Balance at beginning of year	63,249	53,800
Acquisitions		10,386
Foreign currency adjustments	(2,512)	(937)
Balance at end of year	60,737	63,249
Quest Integrity
Goodwill [Line Items]
Balance at beginning of year	30,829	30,535
Foreign currency adjustments	(1,259)	294
Balance at end of year	$ 29,570	$ 30,829