Segment Operations (Financial Information For Reportable Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2011	Nov. 30, 2010	Nov. 30, 2011	Nov. 30, 2010	May 31, 2011
Segment Reporting Information [Line Items]
Net sales	$ 565,652	$ 580,687	$ 1,168,039	$ 1,197,492
Operating income (loss)	2,849	12,924	24,032	33,996
Pre-tax restructuring and other expense (income)	2,048	(76)	3,751	988
Joint venture transactions	(1,192)		2,023
Total assets	1,609,624		1,609,624		1,667,249
Steel Processing [Member]
Segment Reporting Information [Line Items]
Net sales	373,462	317,147	781,636	672,011
Operating income (loss)	7,387	8,429	23,664	25,047
Pre-tax restructuring and other expense (income)		(270)		(373)
Total assets	637,626		637,626		742,838
Pressure Cylinders [Member]
Segment Reporting Information [Line Items]
Net sales	176,717	136,218	345,546	272,292
Operating income (loss)	531	9,523	12,446	19,077
Total assets	553,998		553,998		481,361
Metal Framing [Member]
Segment Reporting Information [Line Items]
Net sales	1,257	77,084	4,402	161,588
Operating income (loss)	372	(6,684)	(3,315)	(10,613)
Pre-tax restructuring and other expense (income)		56		976
Joint venture transactions	(1,192)		2,023
Total assets	13,771		13,771		37,069
Other [Member]
Segment Reporting Information [Line Items]
Net sales	14,216	50,238	36,455	91,601
Operating income (loss)	(5,441)	1,656	(8,763)	485
Pre-tax restructuring and other expense (income)	2,048	138	3,751	385
Total assets	$ 404,229		$ 404,229		$ 405,981