Fair Value - Assets Measured at Fair Value on Non-Recurring Basis (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Aug. 31, 2019	May 31, 2019	Aug. 31, 2018	May 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of ROU assets	$ 4,843
Engineered Cabs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of ROU assets	905
Engineered Cabs Paint Line
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment charge	1,469
Impairment of ROU assets	3,938
Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets estimated fair value	12,860	$ 11,938		$ 11,938
Fair Value, Nonrecurring | CNG fuel system facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets estimated fair value		238		$ 238
Impairment charge		$ 2,167
Fair Value, Nonrecurring | Engineered Cabs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets estimated fair value	$ 12,860
Nisshin
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percent of ownership interest held in unconsolidated affiliates	10.00%	10.00%		10.00%
Impairment charge	$ 4,236			$ 4,017
Nisshin | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets estimated fair value		$ 3,700		3,700
Worthington Aritas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment charge			$ 2,381
Worthington Aritas | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets estimated fair value			7,000
Impairment charge			$ 2,381
Worthington Specialty Processing | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets estimated fair value		1,000		$ 1,000
Impairment charge		$ 3,269