Fair Value - Assets Measured at Fair Value on Non-Recurring Basis (Detail) - USD ($) $ in Thousands		Nov. 30, 2020		May 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis				$ 2,800
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis		$ 6,334		26,984
Fair Value, Measurements, Nonrecurring | Fair Value Inputs Level2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis		6,334		10,561
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis				16,423
Fair Value, Measurements, Nonrecurring | Long Lived Assets Held And Used
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis		6,334	[1]	9,277	[2]
Fair Value, Measurements, Nonrecurring | Long Lived Assets Held And Used | Fair Value Inputs Level2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis		$ 6,334	[1]	6,477	[2]
Fair Value, Measurements, Nonrecurring | Long Lived Assets Held And Used | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis	[2]			2,800
Fair Value, Measurements, Nonrecurring | Investment In Unconsolidated Affiliate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis	[3]			13,623
Fair Value, Measurements, Nonrecurring | Investment In Unconsolidated Affiliate | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis	[3]			13,623
Fair Value, Measurements, Nonrecurring | Long Lived Assets Held For Sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis	[4],[5]			4,084
Fair Value, Measurements, Nonrecurring | Long Lived Assets Held For Sale | Fair Value Inputs Level2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset measured at fair value on non-recurring basis	[4],[5]			$ 4,084

[1] Comprised of our oil & gas equipment assets in Tulsa, Oklahoma with an estimated fair value of $5,934,000, and 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 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] On November 1, 2019, in connection with the contribution of substantially all of the net assets of the Engineered Cabs business to the newly-formed Cabs joint venture, we obtained a 20% minority ownership interest.  In accordance with the applicable accounting guidance, our minority ownership interest in the Cabs joint venture was recorded at its acquisition date fair value of $13,623,000.  

[4] 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.  

[5] 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.