Goodwill and Other Long-Lived Assets - Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Feb. 29, 2020	May 31, 2019		May 31, 2018	May 31, 2020
Goodwill [Line Items]
Goodwill, gross			$ 510,800		$ 521,376	$ 519,724
Impairment losses			(176,193)		(176,193)	(198,290)
Goodwill, net			334,607		345,183	321,434
Acquisitions and purchase accounting adjustments	[1]		11,744		777
Divestitures	[2]		(2,511)		(7,260)
Translation adjustments			(309)		(4,093)
Goodwill, period increase (decrease)			(13,173)		(10,576)
Impairment losses		$ (22,097)	(22,097)	[3]
Steel Processing
Goodwill [Line Items]
Goodwill, gross			7,899		7,899	19,695
Goodwill, net			7,899		7,899	19,695
Acquisitions and purchase accounting adjustments	[1]		11,796
Goodwill, period increase (decrease)			11,796
Pressure Cylinders
Goodwill [Line Items]
Goodwill, gross			330,723		341,299	327,851
Impairment losses			(4,015)		(4,015)	(26,112)
Goodwill, net			326,708		337,284	301,739
Acquisitions and purchase accounting adjustments	[1]		(52)		777
Divestitures	[2]		(2,511)		(7,260)
Translation adjustments			(309)		(4,093)
Goodwill, period increase (decrease)			(24,969)		(10,576)
Impairment losses	[3]		(22,097)
Other
Goodwill [Line Items]
Goodwill, gross			172,178		172,178	172,178
Impairment losses			$ (172,178)		$ (172,178)	$ (172,178)

[1] For additional information regarding the Company’s acquisitions, refer to “Note P – Acquisitions.”

[2] Fiscal 2020 divestitures included the sale of the cryogenics business in Turkey.

[3] Fiscal 2020 impairment losses included $22,097,000 of goodwill impairment related to the oil & gas equipment reporting unit.