Earnings Per Share Calculation - Earnings Per Share Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Oct. 31, 2017	Jul. 31, 2017
Numerator
Net income (loss)	$ 13,856	$ 38,026	$ (459,507)	$ 41,887
Net income (loss) used to calculate Diluted EPS	$ 13,856	$ 42,109	$ (459,507)	$ 42,984
Denominator
Basic weighted average shares outstanding (in shares)	143,975	141,743	143,948	141,223
Add: Shares underlying outstanding stock options and restricted stock units and issuable under employee stock purchase plan (in shares)	1,345	1,317	0	1,409
Dilutive weighted average shares outstanding (in shares)	147,973	165,273	143,948	147,842
EPS
Basic EPS (in dollars per share)	$ 0.10	$ 0.27	$ (3.19)	$ 0.30
Diluted EPS (in dollars per share)	$ 0.09	$ 0.25	$ (3.19)	$ 0.29
0.875% Convertible Senior Notes due June 15, 2017
Numerator
Add: Interest expense associated with convertible senior notes	$ 0	$ 495	$ 0	$ 1,097
Denominator
Add: Shares underlying convertible senior notes (in shares)	0	4,857	0	5,210
EPS
Interest rate on convertible notes (as a percent)					0.875%	0.875%
3.75% Convertible Senior Notes due October 15, 2018 (New)
Denominator
Add: Shares underlying convertible senior notes (in shares)	2,653	0	0	0
EPS
Interest rate on convertible notes (as a percent)	3.75%		3.75%
3.75% Convertible Senior Notes due October 15, 2018 (Original)
Numerator
Add: Interest expense associated with convertible senior notes	$ 0	$ 3,588	$ 0	$ 0
Denominator
Add: Shares underlying convertible senior notes (in shares)	0	17,356	0	0
EPS
Interest rate on convertible notes (as a percent)	3.75%		3.75%