Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Feb. 29, 2012 business	May 31, 2012	May 31, 2011	May 31, 2010
Current:
Federal		$ (9,777)	$ (8,580)	$ 21,649
State		(450)	1,500	1,800
Foreign		2,952	1,800	1,400
Total current		(7,275)	(5,280)	24,849
Deferred		32,755	38,861	(3,863)
Provision for income taxes		25,480	33,581	20,986
Income tax receivable		22,823	9,054
U.S. federal statutory income tax rate (as a percent)		35.00%	35.00%	35.00%
Reasons for difference between the provision for income taxes on pre-tax income from the amount computed by applying the U.S. federal statutory tax rate
Provision for income taxes at the federal statutory rate		32,728	36,193	22,466
Tax benefits on domestic production activities				(1,673)
State income taxes, net of federal benefit and refunds	3,976	(3,465)	910	1,056
Research and development credit		(850)	(350)	(418)
Leveraged lease				(1,517)
Noncontrolling interest		(107)		499
Settlement of tax examinations			(3,531)
Federal adjustments		(3,300)
Other		474	359	573
Provision for income taxes		25,480	33,581	20,986
Deferred tax assets-current attributable to:
Inventory costs		11,268	17,145
Employee benefits		6,036	5,793
Allowance for doubtful accounts		2,114	2,109
AMT, NOL and FTC carrybacks		7,332	8,400
Advanced billings and other		(4,112)	(9,864)
Total net deferred tax assets-current		22,638	23,583
Deferred tax assets-noncurrent attributable to:
Postretirement benefits		19,585	12,847
Bond hedge		3,086	6,733
Foreign intangible assets		39,551
Other		4,765
Total deferred tax assets-noncurrent		66,987	19,580
Total deferred tax assets		89,625	43,163
Deferred tax liabilities attributable to:
Depreciation		(119,049)	(104,202)
Convertible notes		(7,039)	(13,700)
Capitalized program development costs		(17,256)
Foreign intangible assets		(39,551)
Total deferred tax liabilities		(182,895)	(117,902)
Net deferred tax liabilities		(93,270)	(74,739)
Effective income tax rate (as a percent)		27.20%	32.50%
Number of significant businesses relocated	1
Reduction in income tax expense primarily due to allowance of foreign tax credits which had not been previously benefited			$ 3,531