Revenue (Management fee revenue by investment mandate) (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2017
Disaggregation of Revenue by Source [Line Items]
Revenue	$ 1,683,252	$ 1,692,422	$ 1,532,111
Total Management Fees [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	1,463,943	1,459,186	1,309,020
Management Fees: Equity [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	699,726	700,194	634,972
Management Fees: Fixed Income [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	285,388	259,452	249,827
Management Fees: Floating-Rate Income [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	197,695	211,075	186,198
Management Fees: Alternative [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	59,290	85,096	71,095
Management Fees: Portfolio Implementation [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	179,208	159,341	126,379
Management Fees: Exposure Management [Member]
Disaggregation of Revenue by Source [Line Items]
Revenue	$ 42,636	$ 44,028	$ 40,549