Investment (Income) Expense, Net (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011
Component of Other Income, Nonoperating [Line Items]
Interest (income)	$ (1,360)	$ (1,068)	$ (3,593)	$ (3,349)
(Gain) loss on sale of marketable securities	(175)	(3,194)	717	(7,060)
Other-than-temporary impairment on securities	38	57	787	542
Dividend (income)	(693)	(698)	(1,170)	(1,322)
Investment (income) expense, net	$ (2,190)	$ (4,903)	$ (3,259)	$ (11,189)

Income derived from investments in debt securities and on cash and cash equivalents the earnings of which reflect the time value of money or transactions in which the payments are for the use or forbearance of money.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 7

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.7(b))

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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