Impairment of Goodwill and Long-Lived Assets - Additional Information (Detail) - USD ($)		3 Months Ended						9 Months Ended
		Feb. 28, 2021		Nov. 30, 2020	Aug. 31, 2020	Feb. 29, 2020	Aug. 31, 2019	Feb. 28, 2021		Feb. 29, 2020	May 31, 2020
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of goodwill and long-lived assets		$ 0			$ 13,739,000	$ 34,627,000		$ 13,739,000		$ 75,228,000
Net book value of assets		3,137,873,000						3,137,873,000			$ 2,331,515,000
Impairment of long-lived assets		0				34,627,000		13,739,000		75,228,000
Fair market value of assets											2,800,000
Goodwill, Impairment Loss						22,097,000				22,097,000
Operating lease assets		33,245,000						33,245,000			31,557,000
Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets		400,000						400,000			26,984,000
Fair Value, Measurements, Nonrecurring | Fair Value Inputs Level2
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets		400,000						400,000			10,561,000
Cryogenics
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of goodwill and long-lived assets					4,333,000
Impairment of long-lived assets					3,662,000
Jefferson
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of goodwill and long-lived assets					1,423,000
Superior Tools
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of goodwill and long-lived assets					506,000
Oil And Gas Operations
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of long-lived assets						4,679,000
Fixed asset net book value						14,274,000				14,274,000
Intangible Assets Net Book Value						6,577,000
Oil And Gas Operations | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets						3,384,000				3,384,000
Canton | Fair Value Inputs Level2
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of long-lived assets						1,274,000
Fair market value of assets						700,000				700,000
Engineered Cabs
Impaired Long Lived Assets Held And Used [Line Items]
Fixed asset net book value							$ 1,469,000
Impairment of ROU assets							905,000
Operating lease assets							3,938,000
Engineered Cabs | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Impairment of long-lived assets							35,194,000
Long Lived Assets Held And Used | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets		400,000	[1]					400,000	[1]		9,277,000	[2]
Long Lived Assets Held And Used | Fair Value, Measurements, Nonrecurring | Fair Value Inputs Level2
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets		$ 400,000	[1]					$ 400,000	[1]		6,477,000	[2]
Long Lived Assets Held And Used | Oil And Gas Equipment Operations
Impaired Long Lived Assets Held And Used [Line Items]
Net book value of assets				$ 7,375,000
Fair market value of fixed assets				5,934,000
Impairment of long-lived assets				1,441,000
Long Lived Assets Held And Used | Jefferson
Impaired Long Lived Assets Held And Used [Line Items]
Carrying value long-lived assets					1,823,000
Long Lived Assets Held And Used | Jefferson | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets					400,000
Long Lived Assets Held And Used | Engineered Cabs | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets							$ 12,860,000
Finite Lived Intangible Assets | Oil And Gas Equipment Operations
Impaired Long Lived Assets Held And Used [Line Items]
Net book value of assets				$ 2,374,000
Long Lived Assets Held for Sale | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets	[3],[4]										4,084,000
Long Lived Assets Held for Sale | Fair Value, Measurements, Nonrecurring | Fair Value Inputs Level2
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets	[3],[4]										4,084,000
Long Lived Assets Held for Sale | Cryogenics
Impaired Long Lived Assets Held And Used [Line Items]
Carrying value long-lived assets					13,526,000
Long Lived Assets Held for Sale | Cryogenics | Fair Value, Measurements, Nonrecurring
Impaired Long Lived Assets Held And Used [Line Items]
Fair market value of assets					$ 9,193,000
Long Lived Assets Held for Sale | Canton
Impaired Long Lived Assets Held And Used [Line Items]
Net book value of assets						$ 7,775,000				$ 7,775,000	$ 7,813,000

[1] Comprised of our alternative fuel cylinders assets at the Jefferson, Ohio facility with an estimated fair market value of $400,000.  Refer to “NOTE E – Impairment of Goodwill and Long-Lived Assets” for additional information.   

[2] During the fourth quarter of 2020, in connection with the annual indefinite lived assets impairment test, certain European tradenames were written down to their estimated fair market value of $2,800,000.

[3] During the third quarter of fiscal 2020, we committed to a plan to sell the Canton, Michigan facility of our consolidated WSP joint venture and some of the production equipment at that facility.  In accordance with the applicable accounting guidance this production equipment was written down to its estimated fair value of $700,000.  

[4] During the third quarter of fiscal 2020, in connection with the closure of the oil & gas equipment manufacturing operations in Wooster, Ohio, fixed assets consisting of land and a building were written down to their estimated fair market value of $3,384,000.