Consolidated Statements Of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Common Shares	Additional Paid-in Capital USD ($)	Accumulated Other Comprehensive Income (Loss), Net of Tax USD ($)	Retained Earnings USD ($)	Total USD ($)	Noncontrolling Interest USD ($)
Balance at May. 31, 2009	$ 742,963		$ 183,051	$ 4,457	$ 518,561	$ 706,069	$ 36,894
Balance (in shares) at May. 31, 2009		78,997,617
Comprehensive income (loss):
Net earnings	51,507				45,241	45,241	6,266
Unrealized gain on investment	5			5		5
Foreign currency translation	(13,739)			(13,739)		(13,739)
Pension liability adjustment, net of tax of $1,163 in 2010, $(760) in 2011, $4,975 in 2012	317			317		317
Cash flow hedges, net of tax of $854 in 2010, $563 in 2011, $318 in 2012	(1,671)			(1,671)		(1,671)
Total comprehensive income	36,419					30,153	6,266
Common shares issued (in shares)		219,804
Common shares issued	2,291		2,291			2,291
Stock-based compensation	4,576		4,576			4,576
Dividends paid to noncontrolling interest	(4,539)						(4,539)
Cash dividends declared ($0.40 per share in 2010, $0.40 per share in 2011, $0.48 per share in 2012 )	(31,676)				(31,676)	(31,676)
Balance at May. 31, 2010	750,034		189,918	(10,631)	532,126	711,413	38,621
Balance (in shares) at May. 31, 2010		79,217,421
Comprehensive income (loss):
Net earnings	124,034				115,066	115,066	8,968
Foreign currency translation	13,046			13,006		13,006	40
Pension liability adjustment, net of tax of $1,163 in 2010, $(760) in 2011, $4,975 in 2012	1,442			1,442		1,442
Cash flow hedges, net of tax of $854 in 2010, $563 in 2011, $318 in 2012	158			158		158
Total comprehensive income	138,680					129,672	9,008
Acquisition of Nitin Cylinders Limited	14,156						14,156
Common shares issued (in shares)		421,153
Common shares issued	4,827		4,827			4,827
Stock-based compensation	6,173		6,173			6,173
Purchases and retirement of common shares (in shares)	(7,954,698)	(7,954,698)
Purchases and retirement of common shares	(132,764)		(19,393)		(113,371)	(132,764)
Dividends paid to noncontrolling interest	(10,992)						(10,992)
Cash dividends declared ($0.40 per share in 2010, $0.40 per share in 2011, $0.48 per share in 2012 )	(29,411)				(29,411)	(29,411)
Balance at May. 31, 2011	740,703		181,525	3,975	504,410	689,910	50,793
Balance (in shares) at May. 31, 2011		71,683,876
Comprehensive income (loss):
Net earnings	125,353				115,595	115,595	9,758
Foreign currency translation	(17,930)			(14,803)		(14,803)	(3,127)
Pension liability adjustment, net of tax of $1,163 in 2010, $(760) in 2011, $4,975 in 2012	(9,241)			(9,241)		(9,241)
Cash flow hedges, net of tax of $854 in 2010, $563 in 2011, $318 in 2012	(318)			(318)		(318)
Total comprehensive income	97,864					91,233	6,631
Acquisition of Nitin Cylinders Limited	2,333						2,333
Common shares issued (in shares)		689,463
Common shares issued	11,428		11,428			11,428
Stock-based compensation	11,462		11,462			11,462
Purchases and retirement of common shares (in shares)	(4,466,970)	(4,466,970)
Purchases and retirement of common shares	(73,418)		(12,077)		(61,341)	(73,418)
Dividends paid to noncontrolling interest	(9,494)						(9,494)
Cash dividends declared ($0.40 per share in 2010, $0.40 per share in 2011, $0.48 per share in 2012 )	(33,441)				(33,441)	(33,441)
Balance at May. 31, 2012	$ 747,437		$ 192,338	$ (20,387)	$ 525,223	$ 697,174	$ 50,263
Balance (in shares) at May. 31, 2012		67,906,369