Stockholders' Equity (Details) (USD $) In Millions, unless otherwise specified		12 Months Ended								3 Months Ended				3 Months Ended
	Oct. 31, 2012 debtinstrument contracts	Oct. 31, 2012 Minimum [Member] April 2006 Call Spread Option [Member]	Oct. 31, 2012 Minimum [Member] June 2007 Call Spread Option [Member]	Oct. 31, 2012 Maximum [Member] April 2006 Call Spread Option [Member]	Oct. 31, 2012 Maximum [Member] June 2007 Call Spread Option [Member]	Oct. 31, 2012 0.25% Convertible Senior Notes due May 1, 2013 [Member]	Aug. 13, 2012 0.25% Convertible Senior Notes due May 1, 2013 [Member]	Oct. 31, 2011 0.25% Convertible Senior Notes due May 1, 2013 [Member]	Oct. 31, 2010 0.25% Convertible Senior Notes due May 1, 2013 [Member]	Apr. 30, 2006 0.25% Convertible Senior Notes due May 1, 2013 [Member] April 2006 Call Spread Option [Member]	Oct. 31, 2012 0.875% Convertible Senior Notes due June 15, 2017 [Member]	Oct. 31, 2011 0.875% Convertible Senior Notes due June 15, 2017 [Member]	Oct. 31, 2010 0.875% Convertible Senior Notes due June 15, 2017 [Member]	Jul. 31, 2007 0.875% Convertible Senior Notes due June 15, 2017 [Member] June 2007 Call Spread Option [Member]
Option Indexed to Issuer's Equity [Line Items]
Number of call spread option contracts held	2
Number of convertible notes issuances related to call spread options	2
Interest rate on convertible notes						0.25%	0.25%	0.25%	0.25%		0.875%	0.875%	0.875%
Payment for derivative instrument										$ 28.5				$ 42.5
Option indexed to issuer's equity, settlement value in cash or net shares		$ 0	$ 0	$ 45.7	$ 76.1