Revenue (Summary of total revenue by source) (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Disaggregation of Revenue by Source [Line Items]
Total revenue	$ 1,730,365	$ 1,683,252	$ 1,692,422
Management Fees: Sponsored Funds [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	1,012,608	999,256	1,015,263
Management Fees: Seperate Accounts [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	501,780	464,687	443,923
Total Management Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	1,514,388	1,463,943	1,459,186
Distribution And Underwriter Fees: Distribution Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	57,567	63,888	77,402
Distribution And Underwriter Fees: Underwriter Commissions [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	19,489	21,724	19,969
Total Distribution And Underwriter Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	77,056	85,612	97,371
Service Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	131,724	123,073	122,231
Other Revenue [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	$ 7,197	$ 10,624	$ 13,634