Goodwill and Other Long-Lived Assets - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended															12 Months Ended
	Oct. 31, 2012	May. 31, 2015		Feb. 28, 2015		Nov. 30, 2014		Aug. 31, 2014	[1]	May. 31, 2014		Nov. 30, 2013	[1]	Aug. 31, 2013		May. 31, 2013	May. 31, 2015		May. 31, 2014		May. 31, 2013
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets		$ 2,344	[1]	$ 81,600	[1]	$ 14,235	[1]	$ 1,950		$ 22,871	[1]	$ 30,734		$ 4,641	[1]		$ 100,129		$ 58,246		$ 6,488
Expected future severance expense				2,400
Goodwill written-off																	44,933
Goodwill		238,999								251,093						$ 213,858	238,999		251,093		213,858
Asset measured at fair value on nonrecurring basis		12,403								32,074							12,403		32,074
Gain/loss on sale of assets																	2,338		(10,589)
Amortization expense																	$ 20,422		17,386		10,467
Minimum
Goodwill And Other Intangible Assets [Line Items]
Definite-lived intangible assets, estimated useful lives																	1 year
Maximum
Goodwill And Other Intangible Assets [Line Items]
Definite-lived intangible assets, estimated useful lives																	20 years
Non Core Steel Processing Assets
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets																	$ 3,050
Pressure Cylinders
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets	$ 1,520													$ 1,570			11,911		32,005		6,488
Goodwill		226,761								200,509						163,274	226,761		200,509		163,274
Gain/loss on sale of assets	$ 50
Worthington Nitin Cylinders
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets										18,959
Impairment of long-lived assets																4,968
Worthington Nitin Cylinders | Noncontrolling Interest
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets										7,583
Impairment of long-lived assets										7,583						1,987
Long-lived Assets Held and Used
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis		$ 12,403	[2]							7,034	[3]						$ 12,403	[2]	7,034	[3]
Long-lived Assets Held and Used | Worthington Nitin Cylinders
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis										$ 5,925						$ 6,856			$ 5,925		$ 6,856
Joint Venture Transactions | Worthington Nitin Cylinders
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets						6,346
Percent of controlling interest by the Company		60.00%								60.00%							60.00%		60.00%
Impairment of long-lived assets										$ 18,959
Joint Venture Transactions | Long-lived Assets Held and Used | Worthington Nitin Cylinders
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis										5,925									$ 5,925
Engineered Cabs
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets						2,389
Goodwill written-off				44,933
Goodwill				0
Gain(loss)on sale of business				332
Engineered Cabs | Florence Facility
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets				14,311
Asset measured at fair value on nonrecurring basis				9,803
Engineered Cabs | Customer relationships
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets				22,356
Asset measured at fair value on nonrecurring basis				$ 2,000
Aluminum High Pressure Cylinder Business
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets						3,221				1,412
Gain(loss)on sale of business																	$ (2,670)
Aluminum High Pressure Cylinder Business | Long-lived Assets Held and Used
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis										7,034									7,034
Military Construction Business
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets						$ 1,179
CNG Fuel Systems Business
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets		$ 2,344
Zhejiang Nisshin Worthington Precision Specialty Steel Co
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets										7,141
Zhejiang Nisshin Worthington Precision Specialty Steel Co | Long-lived Assets Held and Used
Goodwill And Other Intangible Assets [Line Items]
Net asset										$ 19,115									$ 19,115

[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.