Business Combinations - 2020 Acquisitions (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Apr. 30, 2020	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Business Acquisition [Line Items]
Total purchase consideration		$ 238,300
Goodwill		3,365,114	$ 3,171,179	$ 3,143,249
Design service arrangement	$ 10,700
Design service arrangement, period	5 years
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Total purchase consideration		132,600
Identifiable intangibles assets acquired		44,700
Goodwill		92,800
Semiconductor And System Design
Business Acquisition [Line Items]
Total purchase consideration	$ 105,700
Cash paid	75,700
Consideration transferred, other	30,000
Identifiable intangibles assets acquired	20,600
Recognized identifiable assets acquired and liabilities assumed, net	4,200
Goodwill	$ 80,900	2,939,512	2,758,926	2,730,990
Software Integrity
Business Acquisition [Line Items]
Goodwill		425,602	$ 412,253	$ 412,259
Software Integrity | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Goodwill		$ 13,300