Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Oct. 31, 2020	Jul. 31, 2020	Oct. 31, 2019
Fair Value Measurement [Domain]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments held at cost	$ 20,928
Fair Value Measurement [Domain] | Hexavest [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	11,400
Cash equivalents	291,044		$ 181,907
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
Derivative instruments, assets	4,581		2,075
Assets of consolidated CLO entities: Bank loans and other investments	2,064,133		1,704,270
Total financial assets	3,143,004		2,948,991
Derivative instruments, liabilities	1,279		3,314
Liabilities of consolidated CLO entities: Senior and subordinated note obligations	1,616,243		1,617,095
Total financial liabilities	1,617,522		1,620,409
Hexavest [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Equity securities	11,400	$ 32,700
Debt Securities: Short-term [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	269,802		297,845
Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	180,588		330,966
Debt Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	58,252		55,426
Equity Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	195,510		183,106
Equity Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	35,026		21,236
Equity Securities: Non-consolidated Sponsored Funds And Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	10,497		10,329
Other Assets Not Held At Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0		0
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
Derivative instruments, assets	0		0
Assets of consolidated CLO entities: Bank loans and other investments	0		0
Total financial assets	33,571		161,831
Derivative instruments, liabilities	0		0
Liabilities of consolidated CLO entities: Senior and subordinated note obligations	0		0
Total financial liabilities	0		0
Other Assets Not Held At Fair Value [Member] | Debt Securities: Short-term [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Other Assets Not Held At Fair Value [Member] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Other Assets Not Held At Fair Value [Member] | Debt Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Other Assets Not Held At Fair Value [Member] | Equity Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	0		0
Other Assets Not Held At Fair Value [Member] | Equity Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	0		0
Other Assets Not Held At Fair Value [Member] | Equity Securities: Non-consolidated Sponsored Funds And Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	0		0
Level 1 [Member] | Fair Value Measurement [Domain] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	9,052		24,640
Investments held at cost	0		0
Investments in non-consolidated CLO entities	0		0
Investments in equity method investees	0		0
Derivative instruments, assets	0		0
Assets of consolidated CLO entities: Bank loans and other investments	0		0
Total financial assets	114,133		126,268
Derivative instruments, liabilities	0		0
Liabilities of consolidated CLO entities: Senior and subordinated note obligations	0		0
Total financial liabilities	0		0
Level 1 [Member] | Debt Securities: Short-term [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Level 1 [Member] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Level 1 [Member] | Debt Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Level 1 [Member] | Equity Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	60,308		70,646
Level 1 [Member] | Equity Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	34,925		21,168
Level 1 [Member] | Equity Securities: Non-consolidated Sponsored Funds And Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	9,848		9,814
Level 2 [Member] | Fair Value Measurement [Domain] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	180,588
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	281,992		157,267
Investments held at cost	0		0
Investments in non-consolidated CLO entities	0		0
Investments in equity method investees	0		0
Derivative instruments, assets	4,581		2,075
Assets of consolidated CLO entities: Bank loans and other investments	2,063,423		1,702,769
Total financial assets	2,994,590		2,659,391
Derivative instruments, liabilities	1,279		3,314
Liabilities of consolidated CLO entities: Senior and subordinated note obligations	1,616,243		1,617,095
Total financial liabilities	1,617,522		1,620,409
Level 2 [Member] | Debt Securities: Short-term [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	269,802		297,845
Level 2 [Member] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	269,802		330,966
Level 2 [Member] | Debt Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	58,252		55,426
Level 2 [Member] | Equity Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	135,202		112,460
Level 2 [Member] | Equity Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	101		68
Level 2 [Member] | Equity Securities: Non-consolidated Sponsored Funds And Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	649		515
Level 3 [Member] | Fair Value Measurement [Domain] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0		0
Investments held at cost	0		0
Investments in non-consolidated CLO entities	0		0
Investments in equity method investees	0		0
Derivative instruments, assets	0		0
Assets of consolidated CLO entities: Bank loans and other investments	710		1,501
Total financial assets	710		1,501
Derivative instruments, liabilities	0		0
Liabilities of consolidated CLO entities: Senior and subordinated note obligations	0		0
Total financial liabilities	0		0
Level 3 [Member] | Debt Securities: Short-term [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Level 3 [Member] | Debt Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Level 3 [Member] | Debt Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities, trading	0		0
Level 3 [Member] | Equity Securities: Held By Consolidated Sponsored Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	0		0
Level 3 [Member] | Equity Securities: Held In Separately Managed Accounts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	0		0
Level 3 [Member] | Equity Securities: Non-consolidated Sponsored Funds And Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investment securities	$ 0		$ 0