Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended				1 Months Ended		12 Months Ended		12 Months Ended	1 Months Ended					1 Months Ended		1 Months Ended			1 Months Ended		3 Months Ended		3 Months Ended	1 Months Ended		1 Months Ended			1 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010	Mar. 22, 2012 PSI Energy Solutions, LLC	Mar. 22, 2012 PSI Energy Solutions, LLC Minimum Customer Relationships	Mar. 22, 2012 PSI Energy Solutions, LLC Maximum Customer Relationships	May 31, 2012 Angus	Dec. 29, 2011 Angus	May 31, 2012 Angus Business Acquisition Pro Forma Information	Dec. 29, 2011 Angus Minimum	Dec. 29, 2011 Angus Minimum Customer Relationships	Dec. 29, 2011 Angus Maximum	Dec. 29, 2011 Angus Maximum Customer Relationships	Dec. 02, 2011 Coleman Cylinders	Dec. 02, 2011 Coleman Cylinders Customer Relationships	Sep. 30, 2011 STAKO	Sep. 30, 2011 STAKO Minimum Customer Relationships	Sep. 30, 2011 STAKO Maximum Customer Relationships	Jul. 01, 2011 Bernz	Jul. 01, 2011 Bernz Minimum Customer Relationships	Jul. 01, 2011 Bernz Maximum Customer Relationships	May 31, 2012 MISA Metals, Inc Facility	Mar. 02, 2011 MISA Metals, Inc	May 31, 2012 MISA Metals, Inc Steel Processing Property	Mar. 02, 2011 MISA Metals, Inc Customer Relationships	Dec. 28, 2010 Worthington Nitin Cylinders Limited	Dec. 28, 2010 Worthington Nitin Cylinders Limited Minimum Customer Relationships	Dec. 28, 2010 Worthington Nitin Cylinders Limited Maximum Customer Relationships	Jun. 21, 2010 Hy-Mark Cylinders, Inc	Jun. 21, 2010 Hy-Mark Cylinders, Inc Customer Lists
Business Acquisition [Line Items]
Percentage of outstanding voting interests in acquired entity				75.00%				100.00%																		60.00%
Cash consideration for acquired entity				$ 7,000,000				$ 132,940,000						$ 22,653,000		$ 41,500,000			$ 41,000,000							$ 21,236,000			$ 12,175,000
Assumption of debt related to acquisition								47,324,000
Repayment of debt							44,341,000
Number of restricted common shares issued to former employees								382,749
Vesting period										1 year		3 years
Approximate grant-date fair value of restricted common shares								6,300,000
Amount attributed to purchase price and recognized as goodwill								1,100,000
Amount recognized as stock-based compensation expense	11,742,000	6,173,000	4,570,000				5,200,000
Acquisition-related costs								780,000	508,000
Non-recurring expense									2,347,000
Number of steel processing assets sold																								2
Number of acquired facilities																						3
Total purchase price																							$ 72,600,000
Useful life (Years)					15 years	20 years					10 years		15 years		15 years		10 years	15 years		9 years	13 years				15 years		15 years	20 years		9 years