Fair value measurements - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	$ 1,265,918	$ 1,250,802
Loans	296	653
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	3,451	3,362
Convertibles note, fair value	2,200
Warrants at fair value	1,200
Loans	0	0
Level 3 \| Trade claims
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	0	0
Level 3 \| Private equity funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	17,000
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities owned, at fair value	67,730	62,676
Loans	296	653
Equity method investments	$ 6,100	$ 6,300

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Fair value of financial instruments held by a broker-dealer for their own account (proprietary securities) for trading or investment purposes determined by management based upon quoted prices of a financial instrument with similar characteristics or on a valuation technique or model.

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Fair value portion of warrants not settleable in cash classified as equity.

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