Goodwill and Other Long-Lived Assets - Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
May 31, 2018	May 31, 2017	May 31, 2016
Goodwill [Line Items]
Goodwill, gross	$ 521,376	$ 414,200	$ 412,594
Accumulated impairment losses	(176,193)	(166,527)	(166,527)
Goodwill, net	345,183	247,673	246,067
Acquisitions and purchase accounting adjustments	103,437	854
Translation adjustments	3,739	752
Impairment losses	(9,666)
Goodwill, period increase (decrease)	97,510	1,606
Steel Processing
Goodwill [Line Items]
Goodwill, gross	7,899	7,899	7,045
Goodwill, net	7,899	7,899	7,045
Acquisitions and purchase accounting adjustments		854
Goodwill, period increase (decrease)		854
Pressure Cylinders
Goodwill [Line Items]
Goodwill, gross	341,299	234,123	233,371
Accumulated impairment losses	(4,015)
Goodwill, net	337,284	234,123	233,371
Acquisitions and purchase accounting adjustments	103,437
Translation adjustments	3,739	752
Impairment losses	(4,015)
Goodwill, period increase (decrease)	103,161	752
Engineered Cabs
Goodwill [Line Items]
Goodwill, gross	44,933	44,933	44,933
Accumulated impairment losses	(44,933)	(44,933)	(44,933)
Other
Goodwill [Line Items]
Goodwill, gross	127,245	127,245	127,245
Accumulated impairment losses	(127,245)	(121,594)	(121,594)
Goodwill, net		$ 5,651	$ 5,651
Impairment losses	(5,651)
Goodwill, period increase (decrease)	$ (5,651)

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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