Financial Information for Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended			3 Months Ended		9 Months Ended			1 Months Ended	3 Months Ended			9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2013	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013	May 31, 2013	Feb. 28, 2014 Steel Processing	Feb. 28, 2013 Steel Processing	Feb. 28, 2014 Steel Processing	Feb. 28, 2013 Steel Processing	May 31, 2013 Steel Processing	Oct. 31, 2012 Pressure Cylinders	Feb. 28, 2014 Pressure Cylinders	Aug. 31, 2013 Pressure Cylinders	Feb. 28, 2013 Pressure Cylinders	Feb. 28, 2014 Pressure Cylinders	Feb. 28, 2013 Pressure Cylinders	May 31, 2013 Pressure Cylinders	Feb. 28, 2014 Engineered Cabs	Feb. 28, 2013 Engineered Cabs	Feb. 28, 2014 Engineered Cabs	Feb. 28, 2013 Engineered Cabs	May 31, 2013 Engineered Cabs	Feb. 28, 2014 Other	Feb. 28, 2013 Other	Feb. 28, 2014 Other	Feb. 28, 2013 Other	May 31, 2013 Other
Segment Reporting Information [Line Items]
Net sales	$ 773,230			$ 619,527	$ 2,235,421	$ 1,908,184		$ 477,983	$ 353,879	$ 1,372,558	$ 1,082,998			$ 233,290		$ 205,206	$ 664,212	$ 606,936		$ 51,485	$ 48,628	$ 147,814	$ 170,927		$ 10,472	$ 11,814	$ 50,837	$ 47,323
Operating income (loss)	45,289			33,406	103,426	95,646		28,264	17,701	85,713	48,166			21,278		17,860	49,007	49,965		(1,088)	108	(22,284)	5,367		(3,165)	(2,263)	(9,010)	(7,852)
Restructuring and other expense (income)	1,398			146	(3,781)	1,811		1,380		(3,382)				412		177	(1,035)	183							(394)	(31)	636	1,628
Impairment of long-lived assets		30,734	4,641		35,375	1,520				4,641			1,520		1,570		11,634	1,520				19,100
Joint venture transactions	120			253	1,048	(1,188)																			120	253	1,048	(1,188)
Total assets	$ 2,125,907				$ 2,125,907		$ 1,950,857	$ 856,119		$ 856,119		$ 610,464		$ 780,191			$ 780,191		$ 742,686	$ 176,620		$ 176,620		$ 201,048	$ 312,977		$ 312,977		$ 396,659