Investments (Summary of Investments) (Details) - USD ($) $ in Thousands	Oct. 31, 2019	Oct. 31, 2018
Marketable Securities [Line Items]
Total investment securities held at fair value	$ 898,908	$ 913,352
Investments held at cost	20,904	20,874
Investments in non-consolidated CLO entities	1,417	2,895
Investments in equity method investees	139,510	141,506
Total investments	1,060,739	1,078,627
Debt Securities: Short-term [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	297,845	273,320
Debt and Equity Securities Held by Consolidated Sponsored Funds [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	514,072	540,582
Debt and Equity Securities Held by Separately Managed Accounts [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	76,662	89,121
Non-consolidated Sponsored Funds And Other [Member]
Marketable Securities [Line Items]
Total investment securities held at fair value	$ 10,329	$ 10,329