Fair Value - Valuation of Financial Instruments by Pricing Observability Levels (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 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	$ 8,478	$ 9,385
Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	137,086	146,781
Securities segregated (U.S. Treasury Bills)	771,497	499,245
Derivatives	14,304	20,941
Total assets measured at fair value and other measurements	1,145,202	877,384
Derivatives	19,153	14,944
Contingent consideration liability	8,478	9,385
Total liabilities measured at fair value	27,631	24,329
Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	214,084	201,824
Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Total investments	8,231	8,593
Level 1 | Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	137,086	146,781
Securities segregated (U.S. Treasury Bills)	0	0
Derivatives	876	2,835
Total assets measured at fair value	327,652	351,975
Derivatives	324	33
Contingent consideration liability	0	0
Total liabilities measured at fair value	324	33
Level 1 | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	181,459	193,766
Level 1 | Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Other investments	8,231	8,593
Level 2 | Recurring
Assets, Fair Value Disclosure [Abstract]
Money markets	0	0
Securities segregated (U.S. Treasury Bills)	771,497	499,245
Derivatives	13,428	18,106
Total assets measured at fair value	815,451	523,272
Derivatives	18,829	14,911
Contingent consideration liability	0	0
Total liabilities measured at fair value	18,829	14,911
Level 2 | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	30,526	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	119	121
Derivatives	0	0
Contingent consideration liability	8,478	9,385
Total liabilities measured at fair value	8,478	9,385
Level 3 | Recurring | Equity securities
Assets, Fair Value Disclosure [Abstract]
Equity securities	119	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	1,980	2,016
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	1,980	2,016
NAV Expedient | Recurring | Other investments
Assets, Fair Value Disclosure [Abstract]
Other investments	$ 0	$ 0