Goodwill and Acquired Client Relationships - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Intangible assets
Goodwill impairment			$ 0
Acquired Client Relationships
Estimated Future Amortization Expense of Finite-Lived Intangibles
Indefinite-lived acquired client relationships		$ 0
Closure of Certain Retail Investment Products | Acquired Client Relationships
Estimated Future Amortization Expense of Finite-Lived Intangibles
Indefinite-lived acquired client relationships	$ 0
Acquired Client Relationships
Intangible assets
Amortization and impairment expenses of intangible assets				$ 35,700,000	$ 69,800,000
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible future amortization expense in 2022				50,000,000
Intangible future amortization expense in 2023				50,000,000
Intangible future amortization expense in 2024				35,000,000
Intangible future amortization expense in 2025				30,000,000
Intangible future amortization expense in 2026				30,000,000
Impairment of definite-lived intangible assets				0
Intangible impairments	$ 14,000,000	60,300,000		0	70,700,000
Indefinite-lived acquired client relationships				1,630,300,000	909,000,000.0	$ 972,200,000
Average projected growth rate	(14.00%)
Discount rate for assets based fees	15.00%
Market participant tax rate	25.00%
Acquired Client Relationships | Closure of Certain Retail Investment Products
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible impairments	$ 10,900,000
Acquired Client Relationships | Controlling Interest
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible impairments	12,500,000	$ 32,800,000
Acquired Client Relationships | Controlling Interest | Closure of Certain Retail Investment Products
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible impairments	$ 7,400,000
Acquired Client Relationships | Intangible Amortization and Impairments
Intangible assets
Amortization and impairment expenses of intangible assets				$ 35,700,000	$ 55,300,000	$ 93,400,000