Revenue (Revenue by Source) (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2017
Disaggregation of Revenue by Source [Line Items]
Total revenue	$ 1,683,252	$ 1,692,422	$ 1,532,111
Management Fees: Sponsored Funds [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	999,256	1,015,263	918,539
Management Fees: Seperate Accounts [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	464,687	443,923	390,481
Total Management Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	1,463,943	1,459,186	1,309,020
Distribution And Underwriter Fees: Distribution Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	63,888	77,402	75,762
Distribution And Underwriter Fees: Underwriter Commissions [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	21,724	19,969	19,791
Total Distribution And Underwriter Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	85,612	97,371	95,553
Service Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	123,073	122,231	117,520
Other Revenue [Member]
Disaggregation of Revenue by Source [Line Items]
Total revenue	$ 10,624	$ 13,634	$ 10,018