Investments (Summary of investments) (Details) - USD ($) $ in Thousands	Oct. 31, 2020	Oct. 31, 2019
Marketable Securities [Line Items]
Total investment securities held at fair value	$ 749,675	$ 898,908
Investments held at cost	20,928	20,904
Investments in non-consolidated CLO entities	1,116	1,417
Investments in equity method investees	11,527	139,510
Total investments	783,246	1,060,739
Short-term Debt Securities [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	269,802	297,845
Debt And Equity Securities Held By Consolidated Sponsored Funds [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	376,098	514,072
Debt And Equity Securities Held In Separately Managed Accounts [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	93,278	76,662
Non-consolidated Sponsored Funds And Other [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	$ 10,497	$ 10,329

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