Summary of Significant Accounting Policies - Reconciliation of Weighted Average Common Shares Used to Calculate Basic Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Earnings Per Share [Abstract]
Net income attributed to Synopsys		$ 664,347	$ 532,367	$ 432,518
Weighted average common shares for basic net income per share (in shares)		151,135	149,872	149,036
Dilutive effect of common share equivalents from equity-based compensation (in shares)		4,571	4,318	4,357
Weighted average common shares for diluted net income per share (in shares)		155,706	154,190	153,393
Basic (in USD per share)		$ 4.40	$ 3.55	$ 2.90
Diluted (in USD per share)		$ 4.27	$ 3.45	$ 2.82
Anti-dilutive employee stock-based awards excluded (in shares)	[1]	97	171	850

[1] These stock options and unvested restricted stock units were anti-dilutive for the respective periods and are excluded in calculating diluted net income per share. While such awards were anti-dilutive for the respective periods, they could be dilutive in the future.