Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Voting Common Stock [Member]	Non-Voting Common Stock [Member]	Common Stock [Member]	Common Stock [Member] Voting Common Stock [Member]	Common Stock [Member] Non-Voting Common Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Additional Paid-In Capital [Member] Voting Common Stock [Member]	Additional Paid-In Capital [Member] Non-Voting Common Stock [Member]	Notes Receivable From Stock Option Exercises [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Other Comprehensive Loss [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Loss [Member] Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Retained Earnings [Member] Non-Voting Common Stock [Member]	Non-Redeemable Non-Controlling Interests [Member]	Total Permanent Equity [Member]	Total Permanent Equity [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Total Permanent Equity [Member] Voting Common Stock [Member]	Total Permanent Equity [Member] Non-Voting Common Stock [Member]	Redeemable Non-Controlling Interests [Member]
Beginning balance, (shares) at Oct. 31, 2017				118,521,000
Beginning balance at Oct. 31, 2017					$ 2	$ 461	$ 148,284	$ 675			$ (11,112)	$ (47,474)			$ 921,235	$ (523)		$ 864	$ 1,012,260	$ 152			$ 250,823
Net (income) loss	$ 397,905														381,938			3,049	384,987				12,918
Other comprehensive income (loss), net of tax	(5,707)											(5,707)							(5,707)
Dividends declared															(151,952)				(151,952)
Issuance of Non-Voting Common Stock:
On exercise of stock options (shares)						2,526,000
On exercise of stock options						$ 11				$ 70,156	(1,770)											$ 68,397
Under employee stock purchase plans (shares)						76,000
Under employee stock purchase plans										3,168												3,168
Under employee stock purchase incentive plan (shares)						104,000
Under employee stock purchase incentive plan										4,877												4,877
Under restricted stock plan, net of forfeitures (shares)						1,308,000
Under restricted stock plan, net of forfeitures						$ 5																5
Stock-based compensation							87,047												87,047
Tax benefit (expense) associated with non-controlling interests							5,649												5,649
Repurchase of Non-Voting Common Stock						$ (22)			$ (171)	(286,664)											$ (171)	(286,686)
Repurchase of Common Stock (shares)					(20,000)	(5,564,000)
Principal repayments on notes receivable from stock option exercises											4,825								4,825
Net subscriptions (redemptions/distributions) of non-controlling interest holders																		(2,947)	(2,947)				103,775
Net consolidations (deconsolidations) of sponsored investment funds																							(25,320)
Reclass to temporary equity																		34	34				(34)
Purchase of non-controlling interests																							(22,572)
Changes in redemption value of non-controlling interests redeemable at fair value							(15,507)												(15,507)				15,507
Ending balance at Oct. 31, 2018					$ 2	$ 455	17,514				(8,057)	(53,181)	$ (3,714)	$ (56,895)	1,150,698	$ 3,714		1,000	1,108,431				335,097
Ending balance, (shares) at Oct. 31, 2018				116,951,000
Net (income) loss	432,876														400,035			1,812	401,847				31,029
Other comprehensive income (loss), net of tax	(1,422)											(1,422)							(1,422)
Dividends declared															(162,592)				(162,592)
Issuance of Non-Voting Common Stock:
On exercise of stock options (shares)						1,570,000
On exercise of stock options						$ 6				45,023	(1,573)											43,456
Under employee stock purchase plans (shares)						82,000
Under employee stock purchase plans										3,197												3,197
Under employee stock purchase incentive plan (shares)						126,000
Under employee stock purchase incentive plan										4,594												4,594
Under restricted stock plan, net of forfeitures (shares)						2,247,000
Under restricted stock plan, net of forfeitures						$ 9													9
Stock-based compensation							90,998												90,998
Tax benefit (expense) associated with non-controlling interests							21,944												21,944
Repurchase of Non-Voting Common Stock						(28)				(158,490)							$ 141,416					(299,934)
Repurchase of Common Stock (shares)			(7,409,000)
Principal repayments on notes receivable from stock option exercises											1,183								1,183
Net subscriptions (redemptions/distributions) of non-controlling interest holders																		(2,190)	(2,190)				48,233
Net consolidations (deconsolidations) of sponsored investment funds																							(67,989)
Reclass to temporary equity																		(622)	(622)				622
Purchase of non-controlling interests																							(85,857)
Changes in redemption value of non-controlling interests redeemable at fair value							(24,780)												(24,780)				24,780
Ending balance at Oct. 31, 2019	1,184,119				$ 2	$ 442	0				(8,447)	(58,317)			1,250,439			0	1,184,119				285,915
Ending balance, (shares) at Oct. 31, 2019		422,935	113,143,567	113,567,000
Net (income) loss	133,334														138,516			667	139,183				(5,849)
Other comprehensive income (loss), net of tax	$ (4,959)											(4,959)							(4,959)
Dividends declared															(171,817)				(171,817)
Issuance of Common Stock (shares)					56,000
Issuance of Common Stock									581												581
Issuance of Non-Voting Common Stock:
On exercise of stock options (shares)	3,390,000					3,390,000
On exercise of stock options						$ 13	107,724				(2,187)								105,550
Under employee stock purchase plans (shares)				86,000
Under employee stock purchase plans							3,037												3,037
Under employee stock purchase incentive plan (shares)				114,000
Under employee stock purchase incentive plan							3,973												3,973
Under restricted stock plan, net of forfeitures (shares)				1,625,000
Under restricted stock plan, net of forfeitures						7													7
Stock-based compensation							237,541												237,541
Tax benefit (expense) associated with non-controlling interests							4,216												4,216
Repurchase of Non-Voting Common Stock						$ (16)			$ (145)	$ (171,526)							$ 0				$ (145)	$ (171,542)
Repurchase of Common Stock (shares)		(13,927)			(14,000)	(4,163,000)
Principal repayments on notes receivable from stock option exercises											3,548								3,548
Net subscriptions (redemptions/distributions) of non-controlling interest holders																		(667)	(667)				242,487
Net consolidations (deconsolidations) of sponsored investment funds																							(301,867)
Purchase of non-controlling interests																							(6,772)
Changes in redemption value of non-controlling interests redeemable at fair value							(8,940)												(8,940)				8,940
Ending balance at Oct. 31, 2020	$ 1,323,685				$ 2	$ 446	$ 176,461				$ (7,086)	$ (63,276)			$ 1,217,138			$ 0	$ 1,323,685				$ 222,854
Ending balance, (shares) at Oct. 31, 2020		464,716	114,196,609	114,661,000