Segment Operations (Financial Information For Reportable Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011	May 31, 2011
Segment Reporting Information [Line Items]
Net sales	$ 611,255	$ 569,439	$ 1,779,294	$ 1,766,931
Operating income (loss)	18,075	28,021	42,107	62,017
Pre-tax restructuring and other expense (income)	956	464	4,707	1,452
Joint venture transactions	1,812		3,835
Total assets	1,859,370		1,859,370		1,667,249
Steel Processing [Member]
Segment Reporting Information [Line Items]
Net sales	367,259	301,752	1,148,894	973,763
Operating income (loss)	15,405	14,213	39,069	39,260
Pre-tax restructuring and other expense (income)		70		(303)
Joint venture transactions
Total assets	687,002		687,002		742,838
Pressure Cylinders [Member]
Segment Reporting Information [Line Items]
Net sales	187,737	135,921	533,283	408,213
Operating income (loss)	10,887	10,849	23,333	29,926
Pre-tax restructuring and other expense (income)
Joint venture transactions
Total assets	590,548		590,548		481,361
Engineered Cabs [Member]
Segment Reporting Information [Line Items]
Net sales	40,173		40,173
Operating income (loss)	(1,447)		(1,447)
Pre-tax restructuring and other expense (income)
Joint venture transactions
Total assets	196,466		196,466
Metal Framing [Member]
Segment Reporting Information [Line Items]
Net sales		81,382	4,402	242,970
Operating income (loss)	(2,053)	2,723	(5,368)	(7,890)
Pre-tax restructuring and other expense (income)		411		1,387
Joint venture transactions	1,812		3,835
Total assets	16,297		16,297		37,069
Other [Member]
Segment Reporting Information [Line Items]
Net sales	16,086	50,384	52,542	141,985
Operating income (loss)	(4,717)	236	(13,480)	721
Pre-tax restructuring and other expense (income)	956	(17)	4,707	368
Joint venture transactions
Total assets	$ 369,057		$ 369,057		$ 405,981