Consolidated Statements Of Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss), Net Of Tax [Member]	Retained Earnings [Member]	Total [Member]	Noncontrolling Interest [Member]	Total
Balance at May. 31, 2008		$ 174,900	$ 24,633	$ 685,844	$ 885,377	$ 42,163	$ 927,540
Balance, shares at May. 31, 2008	79,308,056
Comprehensive income (loss):
Net earnings (loss)				(108,214)	(108,214)	4,529	(103,685)
Foreign currency translation			(9,866)		(9,866)	(1,874)	(11,740)
Pension liability adjustment, net of tax			(4,766)		(4,766)		(4,766)
Cash flow hedges, net of tax			(5,544)		(5,544)	(772)	(6,316)
Total comprehensive income (loss)					(128,390)	1,883	(126,507)
Common shares issued		3,875			3,875		3,875
Common shares issued, shares	339,561
Stock-based compensation		5,767			5,767		5,767
Purchases and retirement of common shares		(1,448)		(10,954)	(12,402)		(12,402)
Purchases and retirement of common shares, shares	(650,000)
Dividends paid to noncontrolling interest						(7,152)	(7,152)
Cash dividends declared				(48,115)	(48,115)		(48,115)
Other		(43)			(43)		(43)
Balance at May. 31, 2009		183,051	4,457	518,561	706,069	36,894	742,963
Balance, shares at May. 31, 2009	78,997,617
Comprehensive income (loss):
Net earnings (loss)				45,241	45,241	6,266	51,507
Unrealized gain on investment			5		5		5
Foreign currency translation			(13,739)		(13,739)		(13,739)
Pension liability adjustment, net of tax			317		317		317
Cash flow hedges, net of tax			(1,671)		(1,671)		(1,671)
Total comprehensive income (loss)					30,153	6,266	36,419
Common shares issued		2,291			2,291		2,291
Common shares issued, shares	219,804
Stock-based compensation		4,576			4,576		4,576
Dividends paid to noncontrolling interest						(4,539)	(4,539)
Cash dividends declared				(31,676)	(31,676)		(31,676)
Balance at May. 31, 2010		189,918	(10,631)	532,126	711,413	38,621	750,034
Balance, shares at May. 31, 2010	79,217,421
Comprehensive income (loss):
Net earnings (loss)				115,066	115,066	8,968	124,034
Foreign currency translation			13,006		13,006	40	13,046
Pension liability adjustment, net of tax			1,442		1,442		1,442
Cash flow hedges, net of tax			158		158		158
Total comprehensive income (loss)					129,672	9,008	138,680
Acquisition of Nitin Cylinders Limited						14,156	14,156
Common shares issued		4,827			4,827		4,827
Common shares issued, shares	421,153
Stock-based compensation		6,173			6,173		6,173
Purchases and retirement of common shares		(19,393)		(113,371)	(132,764)		(132,764)
Purchases and retirement of common shares, shares	(7,954,698)
Dividends paid to noncontrolling interest						(10,992)	(10,992)
Cash dividends declared				(29,411)	(29,411)		(29,411)
Balance at May. 31, 2011		$ 181,525	$ 3,975	$ 504,410	$ 689,910	$ 50,793	$ 740,703
Balance, shares at May. 31, 2011	71,683,876