Fair Value Measurements (Details Textual) (4.0% Convertible Senior Notes due March 15, 2015 [Member])	Jul. 31, 2012
4.0% Convertible Senior Notes due March 15, 2015 [Member]
Debt Instrument [Line Items]
Interest rate on convertible notes	4.00%

Interest rate stated in the contractual 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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