Income Per Share Information (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016	Oct. 31, 2016	Sep. 05, 2012
Earnings Per Share [Abstract]
Net income as reported	$ 124,638	$ 89,054	$ 195,054	$ 162,234	$ 382,095
Interest and costs attributable to 0.5% Exchangeable Senior Notes, net of income tax benefit	385	388	769	777
Numerator for diluted earnings per share	$ 125,023	$ 89,442	$ 195,823	$ 163,011
Basic weighted-average shares	163,492	168,952	163,040	171,578
Common stock equivalents	2,051	1,604	2,011	1,967
Shares attributable to 0.5% Exchangeable Senior Notes	5,860	5,858	5,859	5,858
Diluted weighted-average shares	171,403	176,414	170,910	179,403
Debt Instrument [Line Items]
Shares issued under stock incentive and employee stock purchase plans	694	10	1,974	483
0.5% Exchangeable Senior Notes Due 2032 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						0.50%
Restricted Stock Units RSU And Employee Stock Option Member [Member]
Debt Instrument [Line Items]
Weighted-average number of antidilutive options and restricted stock units	1,865	4,364	3,535	3,659