Summary of Consideration Received, Consideration Transferred and Resulting Net Gain on Deconsolidation (Detail) (USD $)	12 Months Ended				1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010	Mar. 02, 2011 MISA Metals, Inc	May 09, 2011 Joint Venture Transactions ArtiFlex	May 31, 2011 Joint Venture Transactions ArtiFlex	Mar. 02, 2011 Joint Venture Transactions ClarkDietrich	May 31, 2011 Joint Venture Transactions ClarkDietrich	Mar. 02, 2011 Joint Venture Transactions ClarkDietrich MISA Metals, Inc
Business Acquisitions and Dispositions [Line Items]
MMI steel processing assets				$ 72,600,000					$ 72,600,000
Interest					28,404,000		58,250,000
Receivable for excess working capital							4,862,000
Cash and other consideration					9,235,000
Total consideration received					37,639,000		135,712,000
Consideration transferred (at book value)					22,599,000		104,393,000
Gain on deconsolidation					15,040,000		31,319,000
Less: Impairment of long-lived assets	355,000	4,386,000	35,409,000		6,414,000	6,414,000	18,293,000	18,293,000
Restructuring charges	5,984,000	2,653,000	4,243,000				11,216,000	11,216,000
Net gain on deconsolidation					$ 8,626,000		$ 1,810,000