Revenue (Summary of Management fee revenue by investment mandate reporting category) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2020	Apr. 30, 2019
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	$ 405,911	$ 411,861	$ 858,465	$ 818,277
Total Management Fees [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	354,121	359,384	748,922	710,134
Management Fees: Equity [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	172,994	172,311	368,747	336,209
Management Fees: Fixed Income [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	61,958	59,105	127,461	117,111
Management Fees: Floating-Rate Income [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	37,563	49,405	80,623	103,083
Management Fees: Alternative [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	12,077	14,128	25,812	30,301
Management Fees: Parametric Custom Portfolios [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	58,360	53,848	123,343	102,755
Management Fees: Parametric Custom Portfolios [Member] | Reclassification Adjustment [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue		9,700		18,700
Management Fees: Parametric Overlay Services [Member]
Disaggregation of Revenue by Investment Mandate [Line Items]
Revenue	$ 11,169	$ 10,587	$ 22,936	$ 20,675