Intangible Assets, net - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2025	Dec. 31, 2024
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 309,290	$ 309,290	$ 290,358
Impairment/Disposals		(600)	0
Accumulated Amortization	(34,609)	(34,609)	(21,795)
Net Carrying Amount	274,081	274,081	268,563
Foreign currency translation differences		3,900	(1,300)
Goodwill, period increase (decrease)		7,879	16,062
Non-amortized intangible assets
Gross Carrying Amount	201,004	201,004
Impairment		(35,000)	(44,900)
Net Carrying Amount	166,004	166,004
Intangible Assets, Gross Carrying Amount	510,294	510,294	536,258
Intangible Assets, Impairment		(35,600)	(44,900)
Intangible Assets, Net Carrying Amount	440,085	440,085	469,563
Kontora Family Office GmbH ("Kontora")
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired		14,800
Adjustments to intangibles		(700)
Pointwise Partners Limited ("PW"), East End Advisors, LLC ("EEA"), And Envoi, LLC (“Envoi”)
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired			99,300
East End Advisors, LLC ("EEA")
Finite-Lived Intangible Assets [Line Items]
Adjustments to intangibles			(4,600)
Envoi Acquisition
Finite-Lived Intangible Assets [Line Items]
Goodwill, period increase (decrease)			(1,000)
Investment management agreements
Non-amortized intangible assets
Gross Carrying Amount	201,000	201,000	245,900
Impairment	(35,000)	(35,000)	(44,900)
Net Carrying Amount	166,000	166,000	$ 201,000
Other intangible asset
Non-amortized intangible assets
Gross Carrying Amount	4	4
Impairment		0
Net Carrying Amount	$ 4	$ 4
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (in years)	22 years	22 years	22 years 3 months 18 days
Gross Carrying Amount	$ 290,262	$ 290,262	$ 277,117
Impairment/Disposals		0	0
Accumulated Amortization	(29,600)	(29,600)	(18,999)
Net Carrying Amount	$ 260,662	$ 260,662	$ 258,118
Investment management agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (in years)	0 years	0 years
Gross Carrying Amount	$ 247	$ 247
Impairment/Disposals		0
Accumulated Amortization	(247)	(247)
Net Carrying Amount	$ 0	$ 0
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (in years)	9 years 3 months 18 days	9 years 3 months 18 days	9 years 4 months 24 days
Gross Carrying Amount	$ 12,280	$ 12,280	$ 11,941
Impairment/Disposals		0	0
Accumulated Amortization	(3,521)	(3,521)	(2,351)
Net Carrying Amount	$ 8,759	$ 8,759	$ 9,590
License
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (in years)	15 years	15 years
Gross Carrying Amount	$ 4,532	$ 4,532
Impairment/Disposals
Accumulated Amortization	(121)	(121)
Net Carrying Amount	$ 4,411	$ 4,411
Acquired internally developed software
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (in years)	5 years	5 years	5 years
Gross Carrying Amount	$ 1,300	$ 1,300	$ 1,300
Impairment/Disposals		(600)	0
Accumulated Amortization	(490)	(490)	(445)
Net Carrying Amount	$ 210	$ 210	$ 855
Other intangible asset
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (in years)	1 year 4 months 24 days	1 year 4 months 24 days
Gross Carrying Amount	$ 669	$ 669
Impairment/Disposals		0
Accumulated Amortization	(630)	(630)
Net Carrying Amount	$ 39	$ 39