Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014
Goodwill [Line Items]
Goodwill, beginning balance	$ 372,687	$ 335,452
Accumulated impairment losses, beginning balance	(121,594)	(121,594)
Goodwill net, beginning balance	251,093	213,858
Acquisitions and purchase accounting adjustments	48,008	36,033
Divestitures	(1,891)
Translation adjustments	(13,278)	1,202
Impairment losses	(44,933)
Goodwill, Period Increase (Decrease)	(12,094)
Goodwill, ending balance	405,526	372,687
Accumulated impairment losses, ending balance	(166,527)	(121,594)
Goodwill net, ending balance	238,999	251,093
Steel Processing
Goodwill [Line Items]
Acquisitions and purchase accounting adjustments	6,587
Goodwill, Period Increase (Decrease)	6,587
Goodwill, ending balance	6,587
Goodwill net, ending balance	6,587
Pressure Cylinders
Goodwill [Line Items]
Goodwill, beginning balance	200,509	163,274
Goodwill net, beginning balance	200,509	163,274
Acquisitions and purchase accounting adjustments	41,421	36,033
Divestitures	(1,891)
Translation adjustments	(13,278)	1,202
Goodwill, Period Increase (Decrease)	26,252
Goodwill, ending balance	226,761	200,509
Goodwill net, ending balance	226,761	200,509
Engineered Cabs
Goodwill [Line Items]
Goodwill, beginning balance	44,933	44,933
Goodwill net, beginning balance	44,933	44,933
Impairment losses	(44,933)
Goodwill, Period Increase (Decrease)	(44,933)
Goodwill, ending balance	44,933	44,933
Accumulated impairment losses, ending balance	(44,933)
Goodwill net, ending balance		44,933
Other
Goodwill [Line Items]
Goodwill, beginning balance	127,245	127,245
Accumulated impairment losses, beginning balance	(121,594)	(121,594)
Goodwill net, beginning balance	5,651	5,651
Goodwill, ending balance	127,245	127,245
Accumulated impairment losses, ending balance	(121,594)	(121,594)
Goodwill net, ending balance	$ 5,651	$ 5,651