Financial Information for Reportable Segments (Detail) (USD $)	3 Months Ended	12 Months Ended
	May 31, 2011	May 31, 2012	May 31, 2011	May 31, 2010
Segment Reporting Information [Line Items]
Net sales		$ 2,534,701,000	$ 2,442,624,000	$ 1,943,034,000
Operating income (loss)		101,610,000	124,356,000	21,963,000
Depreciation and amortization		55,873,000	61,058,000	64,653,000
Pre-tax restructuring and other expense (income)		5,984,000	2,653,000	4,243,000
Pre-tax impairment of long-lived assets		355,000	4,386,000	35,409,000
Joint venture transactions	10,436,000	(150,000)	(10,436,000)
Total assets	1,667,249,000	1,877,797,000	1,667,249,000	1,520,347,000
Steel Processing
Segment Reporting Information [Line Items]
Net sales		1,578,509,000	1,405,492,000	988,950,000
Operating income (loss)		71,578,000	77,671,000	51,353,000
Depreciation and amortization		26,843,000	27,632,000	26,290,000
Pre-tax restructuring and other expense (income)			(303,000)	(488,000)
Joint venture transactions		(2,102,000)
Total assets	742,838,000	703,336,000	742,838,000	674,953,000
Pressure Cylinders
Segment Reporting Information [Line Items]
Net sales		770,101,000	591,945,000	467,572,000
Operating income (loss)		45,108,000	48,954,000	30,056,000
Depreciation and amortization		20,407,000	14,734,000	12,936,000
Pre-tax restructuring and other expense (income)		52,000		309,000
Total assets	481,361,000	575,250,000	481,361,000	393,639,000
Engineered Cabs
Segment Reporting Information [Line Items]
Net sales		104,272,000
Operating income (loss)		4,878,000
Depreciation and amortization		3,540,000
Total assets		199,594,000
Metal Framing
Segment Reporting Information [Line Items]
Net sales		4,402,000	249,543,000	330,578,000
Operating income (loss)		(3,913,000)	(7,530,000)	(10,186,000)
Depreciation and amortization		765,000	9,623,000	14,591,000
Pre-tax restructuring and other expense (income)			1,387,000	3,892,000
Pre-tax impairment of long-lived assets	18,293,000
Joint venture transactions		1,952,000	(1,810,000)
Total assets	37,069,000	7,688,000	37,069,000	203,072,000
Other
Segment Reporting Information [Line Items]
Net sales		77,417,000	195,644,000	155,934,000
Operating income (loss)		(16,041,000)	5,261,000	(49,260,000)
Depreciation and amortization		4,318,000	9,069,000	10,836,000
Pre-tax restructuring and other expense (income)		5,932,000	1,569,000	530,000
Pre-tax impairment of long-lived assets		355,000	4,386,000	35,409,000
Joint venture transactions			(8,626,000)
Total assets	$ 405,981,000	$ 391,929,000	$ 405,981,000	$ 248,683,000