Convertible Notes Payable - Payment of 2013 Convertible Notes (Details) (Point Two Five Percent Convertible Senior Notes Due 2013 [Member], USD $) In Millions, unless otherwise specified	0 Months Ended
May 02, 2013	Jul. 31, 2013
Point Two Five Percent Convertible Senior Notes Due 2013 [Member]
Debt Instrument [Line Items]
Repayments of 2013 convertible notes at maturity	$ 216.2
Interest rate on convertible notes	0.25%	0.25%

The cash outflow from the repayment of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Name:	us-gaap_RepaymentsOfConvertibleDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration