Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, shares in Millions		1 Months Ended		3 Months Ended	12 Months Ended
	Feb. 05, 2026 $ / shares	Dec. 31, 2025 USD ($) jointVenture investment shares	Dec. 31, 2024 USD ($) jointVentureHoldingCompany shares	Dec. 31, 2023 USD ($) investment	Dec. 31, 2025 USD ($) jointVenture investment $ / shares shares	Dec. 31, 2024 USD ($) jointVentureHoldingCompany $ / shares shares	Dec. 31, 2023 USD ($) investment $ / shares	Dec. 31, 2022 USD ($)	Nov. 30, 2024	Apr. 01, 2024 USD ($)
Business Combination [Line Items]
Number of joint venture entities | jointVenture		2			2
Investments owned		$ 531,013,000	$ 535,204,000		$ 531,013,000	$ 535,204,000
Equity Method		255,034,000	286,721,000		255,034,000	286,721,000
Repledged securities		50,200,000	0		50,200,000	0
Collateral advances, allowance		0	0		0	0
Cash on deposit with clearing organization		14,900,000	29,100,000		14,900,000	29,100,000
U.S. Treasury bills pledged as collateral		0	0		0	0
Goodwill		3,598,591,000	3,598,591,000		3,598,591,000	3,598,591,000
Impairment of finite-lived intangible assets				$ 0	$ 4,000,000	$ 4,400,000	$ 0
Impairment, Intangible Asset, Finite-Lived, Statement of Income or Comprehensive Income [Extensible Enumeration]					General and administrative	General and administrative
Impairments of contingent consideration payable					$ 0		0
Contingent consideration liability		8,605,000	9,385,000		8,605,000	$ 9,385,000
Increase (decrease) in contingent consideration payable					0	(130,901,000)	14,050,000
Accounts payable and accrued expenses		381,211,000	426,675,000		381,211,000	426,675,000
Intangible assets, net of accumulated amortization		166,415,000	215,054,000		166,415,000	215,054,000
Finite-lived intangible assets subject to amortization, net		152,900,000	199,800,000		152,900,000	199,800,000
Indefinite-lived intangible assets not subject to amortization		13,500,000	15,300,000		13,500,000	15,300,000
Finite-lived intangible assets		316,600,000	320,800,000		316,600,000	320,800,000
Accumulated amortization of intangible assets		163,700,000	$ 121,000,000.0		163,700,000	121,000,000.0
Amortization of intangible assets					44,918,000	$ 45,913,000	$ 46,854,000
2026		45,000,000			45,000,000
2027		24,000,000			24,000,000
2028		24,000,000			24,000,000
2029		24,000,000			24,000,000
2030		$ 24,000,000			$ 24,000,000
Deferred sales commission amortization period US fund (in years)					1 year
Deferred sales commission amortization period non US funds (in years)					4 years
Period over which receivables from brokers and dealers for sale of shares of company-sponsored mutual funds generally are realized					1 day
Maximum percentage of award an employee can elect to allocate to deferred cash		50.00%	50.00%	50.00%	50.00%	50.00%	50.00%
Maximum amount of deferred cash		$ 250,000	$ 250,000	$ 250,000	$ 250,000	$ 250,000	$ 250,000
Granted to employees and eligible directors | shares		4.2	4.1		5.8	5.9
Net foreign currency transaction gains (losses)					$ 3,500,000	$ 3,700,000	$ 4,500,000
Cash distributions per unit paid to the general partner and unitholders (in dollars per unit) | $ / shares					$ 3.81	$ 3.30	$ 2.92
Subsequent Event
Business Combination [Line Items]
Cash distribution, distribution declared (in dollars per unit) | $ / shares	$ 1.05
Director
Business Combination [Line Items]
Long-term incentive awards vesting periods					3 years
Employees based outside of the United States
Business Combination [Line Items]
Maximum percentage of award an employee can elect to allocate to deferred cash				100.00%			100.00%	100.00%	100.00%
Maximum amount of deferred cash			$ 100,000	$ 100,000		$ 100,000	$ 100,000	$ 100,000
Employees based outside of the United States | Long-term Incentive Compensation Plan, Deferral Limit
Business Combination [Line Items]
Maximum percentage of award an employee can elect to allocate to deferred cash		50.00%			50.00%
Maximum amount of deferred cash		$ 500,000			$ 500,000
Employees based outside of the United States | Long-term Incentive Compensation Plan, Awards Below Deferral Limit
Business Combination [Line Items]
Maximum percentage of award an employee can elect to allocate to deferred cash		100.00%			100.00%
Maximum amount of deferred cash		$ 500,000			$ 500,000
Deferred Sales Commissions
Business Combination [Line Items]
Impairment of finite-lived intangible assets					0	0
CarVal
Business Combination [Line Items]
Goodwill		666,100,000			666,100,000
Business combination, contingent consideration, performance term								6 years
Increase (decrease) in contingent consideration payable						128,500,000
Amount of settlement		134,000,000			134,000,000
Accounts payable and accrued expenses		123,800,000	$ 118,800,000		123,800,000	118,800,000
Sanford C Bernstein Inc Acquisition
Business Combination [Line Items]
Goodwill		2,600,000,000			2,600,000,000
Various smaller acquisitions
Business Combination [Line Items]
Goodwill		$ 291,900,000			$ 291,900,000
Anchorpath
Business Combination [Line Items]
Impairment charge						$ 2,500,000
Autonomous LLC
Business Combination [Line Items]
Transaction costs							28,400,000
Autonomous LLC | Contingent Payment Arrangement Expense
Business Combination [Line Items]
Transaction costs							$ 14,100,000
Business Combination, Separately Recognized Transaction, Acquisition-Related Cost, Expensed, Statement of Income or Comprehensive Income [Extensible Enumeration]							Contingent payment arrangements
Autonomous LLC | Compensation and Benefits Expense
Business Combination [Line Items]
Transaction costs							$ 14,300,000
Business Combination, Separately Recognized Transaction, Acquisition-Related Cost, Expensed, Statement of Income or Comprehensive Income [Extensible Enumeration]							Labor and Related Expense
Minimum
Business Combination [Line Items]
Intangible assets acquired, estimated useful life		5 years			5 years
Minimum | Employee
Business Combination [Line Items]
Long-term incentive awards vesting periods					3 years
Minimum | CarVal
Business Combination [Line Items]
Contingent consideration liability								$ 0
Maximum
Business Combination [Line Items]
Intangible assets acquired, estimated useful life		20 years			20 years
Maximum | Employee
Business Combination [Line Items]
Long-term incentive awards vesting periods					4 years
Maximum | CarVal
Business Combination [Line Items]
Contingent consideration liability								$ 650,000,000
Furniture
Business Combination [Line Items]
Useful life (in years)		8 years			8 years
Equipment | Minimum
Business Combination [Line Items]
Useful life (in years)		3 years			3 years
Equipment | Maximum
Business Combination [Line Items]
Useful life (in years)		6 years			6 years
AB | AB Holding
Business Combination [Line Items]
General partnership interest in company (percent)					1.00%
Joint Venture
Business Combination [Line Items]
Number of joint venture entities		2	2	2	2	2	2
Investments owned										$ 283,900,000
Equity Method		$ 247,600,000			$ 247,600,000
Joint Venture, North America
Business Combination [Line Items]
Interest in the joint venture		66.70%			66.70%					66.70%
Joint Venture, International
Business Combination [Line Items]
Interest in the joint venture		49.00%			49.00%