Summary of Hedge Notes (Parenthetical) (Detail)	Jul. 31, 2013 0.75% Convertible Senior Notes due January 15, 2015	Jan. 31, 2010 0.75% Convertible Senior Notes due January 15, 2015	Jul. 31, 2013 0.25% Convertible Senior Notes due April 1, 2018	Mar. 31, 2013 0.25% Convertible Senior Notes due April 1, 2018
Derivatives, Fair Value [Line Items]
Note, Interest Rate	0.75%	0.75%	0.25%	0.25%

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: 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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