Long-term Debt - Summary of 4 1/16% Debentures Repurchased (Parenthetical) (Details)	May. 31, 2015	May. 31, 2014
4 1/16% Convertible Subordinated Debentures [Member]
Debt Instrument [Line Items]
Debt instrument interest rate stated percentage	4.0625%	4.0625%

Contractual interest rate for funds borrowed, under the debt agreement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant