Revenue (Summary of management fee revenue by investment mandate reporting category) (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2018
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	$ 1,730,365	$ 1,683,252	$ 1,692,422
Total Management Fees [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	1,514,388	1,463,943	1,459,186
Management Fees: Equity [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	742,491	699,726	700,194
Management Fees: Fixed Income [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	265,263	244,564	229,115
Management Fees: Floating-Rate Income [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	151,928	197,695	211,075
Management Fees: Alternative [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	51,045	59,290	85,096
Management Fees: Parametric Custom Portfolios [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	257,125	220,032	189,678
Management Fees: Parametric Custom Portfolios [Member] | Reclassification Adjustment [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue		40,800	30,300
Management Fees: Parametric Overlay Services [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	$ 46,536	$ 42,636	$ 44,028