Assets Measured at Fair Value on Non-recurring Basis (Parenthetical) (Detail) (USD $)	3 Months Ended			6 Months Ended			3 Months Ended
	Nov. 30, 2014		Nov. 30, 2013	Nov. 30, 2014		Nov. 30, 2013	May 31, 2014
Fair Value [Line Items]
Impairment of long-lived assets	$ 14,235,000		$ 30,734,000	$ 16,185,000		$ 35,375,000
Asset measured at fair value on nonrecurring basis	25,571,000			25,571,000			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%
Military Construction Business
Fair Value [Line Items]
Impairment of long-lived assets	1,179,000
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	3,221,000						1,412,000
Zhejiang Nisshin Worthington Precision Specialty Steel Co
Fair Value [Line Items]
Impairment of long-lived assets							7,141,000
Non Core Steel Processing Assets
Fair Value [Line Items]
Impairment of long-lived assets				3,050,000
Custom Plastics And Interior Components Business
Fair Value [Line Items]
Impairment of long-lived assets	2,389,000
Long-lived assets held and used
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis	3,750,000	[1]		3,750,000	[1]		7,034,000	[2]
Long-lived assets held and used | Worthington Nitin Cylinders
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis							5,925,000
Long-lived assets held and used | Global Group
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis	3,221,000			3,221,000			7,034,000
Long-lived assets held and used | Zhejiang Nisshin Worthington Precision Specialty Steel Co
Fair Value [Line Items]
Net asset							19,115,000
Long-lived assets held and used | Non Core Steel Processing Assets
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis	19,402,000			19,402,000
Long-lived assets held and used | Custom Plastics And Interior Components Business
Fair Value [Line Items]
Asset measured at fair value on nonrecurring basis	$ 2,419,000			$ 2,419,000

[1] During the second quarter of fiscal 2015, 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 $3,750,000, resulting in an impairment charge of $3,221,000 during the three months ended November 30, 2014. During the second quarter of fiscal 2015, we determined that indicators of impairment were present at the Company's military construction business. 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, resulting in an impairment charge of $1,179,000 during the three months ended November 30, 2014, which represents the remaining book value of the asset group. During the fourth quarter of fiscal 2014, management committed to a plan to sell the Company's 60%-owned consolidated joint venture in India, Worthington Nitin Cylinders. As all of the criteria for classification as assets held for sale were met, the net assets of the business were presented separately as assets held for sale in our consolidated balance sheet as of May 31, 2014. In accordance with the applicable accounting guidance, the net assets were recorded at the lower of net book value or fair value less costs to sell as of May 31, 2014. As a result of changes in facts and circumstances related to the planned sale of Worthington Nitin Cylinders during the second quarter of fiscal 2015, the Company reassessed the fair value of the business and determined that the remaining book value should be written off resulting in an impairment charge of $6,346,000.

[2] 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.