Goodwill and Other Long-Lived Assets - Additional Information (Detail)		3 Months Ended														6 Months Ended	12 Months Ended
		Nov. 30, 2015 USD ($) Facility		Aug. 31, 2015 USD ($)		May 31, 2015 USD ($)		Feb. 28, 2015 USD ($)		Nov. 30, 2014 USD ($)		Aug. 31, 2014 USD ($)	[1]	May 31, 2014 USD ($)	Nov. 30, 2013 USD ($)	Nov. 30, 2015 USD ($)	May 31, 2016 USD ($)	May 31, 2015 USD ($)	May 31, 2014 USD ($)
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis						$ 12,403,000											$ 0	$ 12,403,000
Impairment of long-lived assets		$ 22,962,000	[1]	$ 3,000,000	[1]	2,344,000	[1]	$ 81,600,000	[1]	$ 14,235,000	[1]	$ 1,950,000			$ 30,734,000		25,962,000	100,129,000	$ 58,246,000
Goodwill						238,999,000								$ 251,093,000			246,067,000	238,999,000	251,093,000
Goodwill written-off																		44,933,000
Amortization expense																	$ 15,813,000	20,422,000	17,386,000
DHybrid Systems LLC
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis						600,000												600,000
Impairment of long-lived assets						2,344,000
Goodwill						17,822,000												17,822,000
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
Long-lived Assets Held and Used
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis	[2]					12,403,000												12,403,000
Engineered Cabs
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets				3,000,000						2,389,000							$ 3,000,000	83,989,000	19,100,000
Goodwill								0						44,933,000					44,933,000
Goodwill written-off								44,933,000										44,933,000
Gain (loss) on sale of business								332,000
Engineered Cabs | Florence Facility
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis								9,803,000
Impairment of long-lived assets								14,311,000
Engineered Cabs | Customer relationships
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis								2,000,000
Impairment of long-lived assets								$ 22,356,000
Engineered Cabs | Long-lived Assets Held and Used
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis				1,059,000
Carrying value long-lived assets				$ 4,059,000
Pressure Cylinders
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets																	22,962,000	11,911,000	32,005,000
Goodwill						226,761,000								200,509,000			233,371,000	226,761,000	$ 200,509,000
Pressure Cylinders | Aluminum High Pressure Cylinder Business
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets										3,221,000				1,412,000
Pressure Cylinders | Oil & Gas Equipment
Goodwill And Other Intangible Assets [Line Items]
Number of equipment facilities | Facility		2
Carrying value long-lived assets		$ 59,895,000
Cash flow projections, discount rate		13.00%
Impairment of long-lived assets		$ 22,962,000
Goodwill		25,982,000														$ 25,982,000
Pressure Cylinders | Worthington Nitin Cylinders
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets														18,959,000
Pressure Cylinders | Worthington Nitin Cylinders | Noncontrolling Interest
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets														$ 7,583,000
Pressure Cylinders | Worthington Nitin Cylinders | Joint Venture Transactions
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets																6,346,000
Percent of controlling interest by the Company														60.00%					60.00%
Pressure Cylinders | Long-lived Assets Held and Used | Aluminum High Pressure Cylinder Business
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis														$ 7,034,000					$ 7,034,000
Pressure Cylinders | Long-lived Assets Held and Used | Oil & Gas Equipment
Goodwill And Other Intangible Assets [Line Items]
Asset measured at fair value on nonrecurring basis		$ 36,933,000														36,933,000
Other Business Segment | Military Construction Business
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets										$ 1,179,000
Steel Processing
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets																		3,050,000	$ 7,141,000
Goodwill						$ 6,587,000											$ 7,045,000	$ 6,587,000
Steel Processing | Closure of Precision Specialty Metals, Inc
Goodwill And Other Intangible Assets [Line Items]
Impairment of long-lived assets														$ 7,141,000		$ 3,050,000

[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.