Fair Value - Valuation of Financial Instruments by Pricing Observability Levels (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Assets, Fair Value Disclosure [Abstract]
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Brokers and dealers	Brokers and dealers
Derivative Liability, Statement Of Financial Position, Extensible Enumeration, Not Disclosed Flag	Derivatives	Derivatives
Contingent consideration liability	$ 8,520	$ 9,385
Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	133,750	146,781
Securities segregated (U.S. Treasury Bills)	481,760	499,245
Derivatives	27,050	20,941
Total assets measured at fair value and other measurements	841,656	877,384
Short equities – corporate	707
Derivatives	30,077	14,944
Contingent consideration liability	8,520	9,385
Total liabilities measured at fair value	39,304	24,329
Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	190,056	201,824
Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Total investments	9,040	8,593
Level 1 | Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	133,750	146,781
Securities segregated (U.S. Treasury Bills)	0	0
Derivatives	322	2,835
Total assets measured at fair value	298,177	351,975
Short equities – corporate	707
Derivatives	2,582	33
Contingent consideration liability	0	0
Total liabilities measured at fair value	3,289	33
Level 1 | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	155,065	193,766
Level 1 | Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Other investments	9,040	8,593
Level 2 | Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	0	0
Securities segregated (U.S. Treasury Bills)	481,760	499,245
Derivatives	26,728	18,106
Total assets measured at fair value	541,202	523,272
Short equities – corporate	0
Derivatives	27,495	14,911
Contingent consideration liability	0	0
Total liabilities measured at fair value	27,495	14,911
Level 2 | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	32,714	5,921
Level 2 | Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Other investments	0	0
Level 3 | Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	0	0
Securities segregated (U.S. Treasury Bills)	0	0
Derivatives	0	0
Total assets measured at fair value	121	121
Short equities – corporate	0
Derivatives	0	0
Contingent consideration liability	8,520	9,385
Total liabilities measured at fair value	8,520	9,385
Level 3 | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	121	121
Level 3 | Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Other investments	0	0
NAV Expedient | Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	0	0
Securities segregated (U.S. Treasury Bills)	0	0
Derivatives	0	0
Total assets measured at fair value	2,156	2,016
Short equities – corporate	0
Derivatives	0	0
Contingent consideration liability	0	0
Total liabilities measured at fair value	0	0
NAV Expedient | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	2,156	2,016
NAV Expedient | Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Other investments	$ 0	$ 0