Acquisitions, Goodwill and Intangible Assets (Narrative) (Details)	3 Months Ended	12 Months Ended
	Oct. 31, 2020 USD ($)	Oct. 31, 2020 USD ($)	Oct. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)
Business Acquisition [Line Items]
Goodwill	$ 259,681,000	$ 259,681,000	$ 259,681,000
Goodwill impairment		0	0	$ 0
Impairment of amortization or non-amortizing intangible assets		0	0	0
Intangible assets amortization expense		3,800,000	$ 5,000,000.0	8,900,000
Future Amortization Expense, Year One	5,505,000	5,505,000
Future Amortization Expense, Year Two	5,377,000	5,377,000
Future Amortization Expense, Year Three	4,977,000	4,977,000
Future Amortization Expense, Year Four	4,902,000	4,902,000
Future Amortization Expense, Year Five	$ 4,862,000	$ 4,862,000
Client Relationships [Member]
Business Acquisition [Line Items]
Weighted-average remaining amortization period (in years)		13 years 8 months 12 days	9 years 6 months
Assembled Workforce [Member]
Business Acquisition [Line Items]
Weighted-average remaining amortization period (in years)		15 years
Trademark [Member]
Business Acquisition [Line Items]
Weighted-average remaining amortization period (in years)		10 years 1 month 6 days	11 years 1 month 6 days
Atlanta Capital [Member]
Business Acquisition [Line Items]
Total Non-controlling profits interests (direct and indirect) held by interest holders at the end of period	7.10%	7.10%	8.20%
Amount paid for indirect profit interest pursuant to the call option provisions of the Long-term Equity Incentive Plan		$ 6,800,000	$ 7,800,000	$ 8,200,000
Estimated fair value of noncontrolling interests	$ 27,400,000	27,400,000	25,200,000
Parametric Portfolio Associates [Member]
Business Acquisition [Line Items]
Estimated fair value of noncontrolling interests			73,500,000
Parametric Portfolio Associates [Member] | Parametric Risk Advisors [Member]
Business Acquisition [Line Items]
Estimated fair value of noncontrolling interests			12,300,000
Parametric Portfolio Associates [Member] | Parametric Plan [Member]
Business Acquisition [Line Items]
Estimated fair value of noncontrolling interests			$ 61,200,000
Wateroak Advisors, LLC [Member]
Business Acquisition [Line Items]
Total cost to acquire company	48,100,000
Cash paid in business acquisition	28,800,000
Incurred contingent liability	19,300,000
Intangible assets amortization expense		0
Future Amortization Expense, Year One	16,100,000	16,100,000
Future Amortization Expense, Year Two	16,100,000	16,100,000
Future Amortization Expense, Year Three	16,100,000	16,100,000
Future Amortization Expense, Year Four	16,100,000	16,100,000
Future Amortization Expense, Year Five	$ 16,100,000	$ 16,100,000
Wateroak Advisors, LLC [Member] | Risk-Free Rate [Member]
Business Acquisition [Line Items]
Key assumptions percent	0.0025	0.0025
Wateroak Advisors, LLC [Member] | Client Relationships [Member]
Business Acquisition [Line Items]
Intangible assets acquired	$ 46,600,000	$ 46,600,000
Weighted-average remaining amortization period (in years)		15 years
Wateroak Advisors, LLC [Member] | Assembled Workforce [Member]
Business Acquisition [Line Items]
Intangible assets acquired	1,000,000.0	$ 1,000,000.0
Weighted-average remaining amortization period (in years)		15 years
Wateroak Advisors, LLC [Member] | Trademark [Member]
Business Acquisition [Line Items]
Intangible assets acquired	$ 500,000	$ 500,000
Weighted-average remaining amortization period (in years)		10 years