Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Voting Common Stock [Member]	Non-Voting 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] Voting Common Stock [Member]	Additional Paid-In Capital [Member] Non-Voting Common Stock [Member]	Notes Receivable From Stock Option Exercises [Member]	Notes Receivable From Stock Option Exercises [Member] Non-Voting Common Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Retained Earnings [Member] Non-Voting Common Stock [Member]	Non-Redeemable Non-Controlling Interests [Member]	Total Permanent Equity [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 at Oct. 31, 2018				$ 2	$ 455	$ 17,514			$ (8,057)		$ (53,181)	$ 1,150,698		$ 1,000	$ 1,108,431			$ 335,097
Net income	$ 205,390											188,608		862	189,470			15,920
Other comprehensive loss, net of tax	(4,720)										(4,720)				(4,720)
Dividends declared												(80,425)			(80,425)
Issuance of Non-Voting Common Stock:
On exercise of stock options					2			$ 12,029		$ (248)							$ 11,783
Under employee stock purchase plans								1,593									1,593
Under employee stock purchase incentive plan								3,389									3,389
Under restricted stock plan, net of forfeitures					7												7
Stock-based compensation						44,547									44,547
Tax benefit (expense) of non-controlling interest						959									959
Repurchase of Non-Voting Common Stock					(18)			(78,887)					$ (104,625)				(183,530)
Principal repayments on notes receivable from stock option exercises									485						485
Net subscriptions (redemptions/distributions) of non-controlling interest holders														(841)	(841)			43,919
Net consolidations (deconsolidations) of sponsored investment funds																		(51,912)
Reclass to temporary equity														28	28			(28)
Purchase of non-controlling interests																		(3,964)
Changes in redemption value of non-controlling interests redeemable at fair value						(1,144)									(1,144)			1,144
Ending balance at Apr. 30, 2019				2	446	0			(7,820)		(61,615)	1,157,970		1,049	1,090,032			340,176
Beginning balance at Jan. 31, 2019				2	450	0			(7,875)		(55,933)	1,131,094		1,006	1,068,744			326,589
Net income	113,130											101,807		445	102,252			10,878
Other comprehensive loss, net of tax	(5,682)										(5,682)				(5,682)
Dividends declared												(40,039)			(40,039)
Issuance of Non-Voting Common Stock:
On exercise of stock options					1			9,049		(49)							9,001
Under employee stock purchase incentive plan								2,917									2,917
Under restricted stock plan, net of forfeitures					1												1
Stock-based compensation						21,888									21,888
Tax benefit (expense) of non-controlling interest						(33)									(33)
Repurchase of Non-Voting Common Stock					(6)	(33,599)						(34,892)			(68,497)
Principal repayments on notes receivable from stock option exercises									104						104
Net subscriptions (redemptions/distributions) of non-controlling interest holders														(402)	(402)			2,698
Net consolidations (deconsolidations) of sponsored investment funds																		(211)
Changes in redemption value of non-controlling interests redeemable at fair value						(222)									(222)			222
Ending balance at Apr. 30, 2019				2	446	0			(7,820)		(61,615)	1,157,970		1,049	1,090,032			340,176
Cumulative effect adjustment upon adoption of new accounting standard (ASU 2016-01)											(3,714)	3,714
Beginning balance, (shares) at Oct. 31, 2019		422,935	113,143,567
Beginning balance at Oct. 31, 2019	1,184,119			2	442	0			(8,447)		(58,317)	1,250,439		0	1,184,119			285,915
Net income	140,891											176,043		366	176,409			(35,518)
Other comprehensive loss, net of tax	(10,608)										(10,608)				(10,608)
Dividends declared												(85,923)			(85,923)
Issuance of Common Stock							$ 581									$ 581
Issuance of Non-Voting Common Stock:
On exercise of stock options					5			46,409		(1,081)							45,333
Under employee stock purchase plans								1,657									1,657
Under employee stock purchase incentive plan					1			2,966									2,967
Under restricted stock plan, net of forfeitures					6												6
Stock-based compensation						50,951									50,951
Tax benefit (expense) of non-controlling interest						2,509									2,509
Repurchase of Non-Voting Common Stock					(9)			(97,588)									(97,597)
Principal repayments on notes receivable from stock option exercises									2,458						2,458
Net subscriptions (redemptions/distributions) of non-controlling interest holders														(366)	(366)			117,926
Net consolidations (deconsolidations) of sponsored investment funds																		(152,579)
Changes in redemption value of non-controlling interests redeemable at fair value						4,609									4,609			(4,609)
Ending balance at Apr. 30, 2020	1,277,105			2	445	12,094			(7,070)		(68,925)	1,340,559		0	1,277,105			211,135
Ending balance, (shares) at Apr. 30, 2020		478,643	113,929,794
Beginning balance at Jan. 31, 2020				2	446	0			(7,354)		(58,701)	1,310,631		0	1,245,024			336,087
Net income	28,056											72,058		159	72,217			(44,161)
Other comprehensive loss, net of tax	(10,224)										(10,224)				(10,224)
Dividends declared												(42,875)			(42,875)
Issuance of Non-Voting Common Stock:
On exercise of stock options					1			14,674		$ (959)							13,716
Under employee stock purchase incentive plan					1			271									272
Stock-based compensation						21,431									21,431
Tax benefit (expense) of non-controlling interest						2,523									2,523
Repurchase of Non-Voting Common Stock					(3)			$ (31,718)					$ 745				$ (30,976)
Principal repayments on notes receivable from stock option exercises									1,243						1,243
Net subscriptions (redemptions/distributions) of non-controlling interest holders														(159)	(159)			76,701
Net consolidations (deconsolidations) of sponsored investment funds																		(152,579)
Changes in redemption value of non-controlling interests redeemable at fair value						4,913									4,913			(4,913)
Ending balance at Apr. 30, 2020	$ 1,277,105			$ 2	$ 445	$ 12,094			$ (7,070)		$ (68,925)	$ 1,340,559		$ 0	$ 1,277,105			$ 211,135
Ending balance, (shares) at Apr. 30, 2020		478,643	113,929,794