Assets Measured at Fair Value on Non-recurring Basis (Parenthetical) (Detail) - USD ($)	3 Months Ended														12 Months Ended
	May. 31, 2015		Feb. 28, 2015		Nov. 30, 2014		Aug. 31, 2014	[1]	May. 31, 2014		Nov. 30, 2013	[1]	Aug. 31, 2013	[1]	May. 31, 2015		May. 31, 2014		May. 31, 2013
Fair Value [Line Items]
Impairment of long-lived assets	$ 2,344,000	[1]	$ 81,600,000	[1]	$ 14,235,000	[1]	$ 1,950,000		$ 22,871,000	[1]	$ 30,734,000		$ 4,641,000		$ 100,129,000		$ 58,246,000		$ 6,488,000
Asset measured at fair value on nonrecurring basis	$ 12,403,000								32,074,000						$ 12,403,000		$ 32,074,000
Worthington Nitin Cylinders
Fair Value [Line Items]
Impairment of long-lived assets									$ 18,959,000
Worthington Nitin Cylinders | Joint Venture Transactions
Fair Value [Line Items]
Impairment of long-lived assets					6,346,000
Ownership interest in joint venture	60.00%								60.00%						60.00%		60.00%
Zhejiang Nisshin Worthington Precision Specialty Steel Co
Fair Value [Line Items]
Impairment of long-lived assets									$ 7,141,000
Engineered Cabs
Fair Value [Line Items]
Impairment of long-lived assets					$ 2,389,000
Customer relationships | Engineered Cabs
Fair Value [Line Items]
Impairment of long-lived assets			22,356,000
Asset measured at fair value on nonrecurring basis			2,000,000
DHybrid Systems Llc
Fair Value [Line Items]
Impairment of long-lived assets	$ 2,344,000
Asset measured at fair value on nonrecurring basis	600,000														$ 600,000
Noncontrolling Interest | Worthington Nitin Cylinders
Fair Value [Line Items]
Impairment of long-lived assets									7,583,000
Global Group
Fair Value [Line Items]
Impairment of long-lived assets									1,412,000
Florence Facility | Engineered Cabs
Fair Value [Line Items]
Impairment of long-lived assets			14,311,000
Asset measured at fair value on nonrecurring basis			$ 9,803,000
Long-lived Assets Held and Used
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis	$ 12,403,000	[2]							7,034,000	[3]					$ 12,403,000	[2]	$ 7,034,000	[3]
Long-lived Assets Held and Used | Worthington Nitin Cylinders
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis									5,925,000								5,925,000		$ 6,856,000
Long-lived Assets Held and Used | Worthington Nitin Cylinders | Joint Venture Transactions
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis									5,925,000								5,925,000
Long-lived Assets Held and Used | Zhejiang Nisshin Worthington Precision Specialty Steel Co
Fair Value [Line Items]
Net asset									19,115,000								19,115,000
Long-lived Assets Held and Used | Global Group
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis									$ 7,034,000								$ 7,034,000

[1] For additional information regarding the Company's impairment charges, refer to "Note C - Goodwill and Other Long-Lived Assets."

[2] During the fourth quarter of fiscal 2015, the Company determined that indicators of impairment were present with regard to intangible assets related to our CNG fuel systems joint venture, dHybrid. Recoverability of the identified asset group was tested using future cash flow projections based on management's long-range estimates of market conditions. The sum of these undiscounted future cash flows was less than the net book value of the asset group. In accordance with the applicable accounting guidance, the intangible assets were written down to their fair value of $600,000, resulting in an impairment charge of $2,344,000. The key assumptions that drove the fair value calculation were projected cash flows and the discount rate. During the third quarter of fiscal 2015, the Company concluded that an interim impairment test of the goodwill of its Engineered Cabs operating segment was necessary. Prior to conducting the goodwill impairment test, the Company first evaluated the other long-lived assets of the Engineered Cabs operating segment for recoverability. Recoverability was tested using future cash flow projections based on management's long-range estimates of market conditions. The sum of the undiscounted future cash flows for the customer relationship intangible asset and the property, plant and equipment of the Florence, South Carolina facility were less than their respective carrying values. As a result, these assets were written down to their respective fair values of $2,000,000 and $9,803,000. The fair value measurements are based on significant inputs not observable in the market and thus represent Level 3 measurements. The key assumptions that drove the fair value calculations were projected cash flows and the discount rate.

[3] During the fourth quarter of fiscal 2014, we determined that indicators of impairment were present at the Company's aluminum high-pressure cylinder business in New Albany, Mississippi, due to current and projected operating losses. Recoverability of the identified asset group was tested using future cash flow projections based on management's long-range estimates of market conditions. The sum of these undiscounted future cash flows was less than the net book value of the asset group. In accordance with the applicable accounting guidance, the net assets were written down to their fair value of $7,034,000, resulting in an impairment charge of $1,412,000 within impairment of long-lived assets in our fiscal 2014 consolidated statement of earnings. Market observable, Level 2 inputs are used to determine fair value.