v3.26.1
Collateralized transactions - Narrative (Details)
 6 Months Ended
Jun. 30, 2026
USD ($)
dealer
customer
Dec. 31, 2025
USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Bank call loans $ 349,900,000 $ 76,800,000
Market value of securities 37,500,000 352,000,000.0
Customer securities under customer margin loans that are available to be pledged 2,100,000,000  
Re-pledged amounts under securities loans agreements 333,700,000  
Customer securities directly with the Options Clearing Corporation to secure obligations and margin requirements under option contracts written by customers 770,900,000  
Outstanding letters of credit 0  
Amounts pledged $ 1,226,378,000 1,179,503,000
Number of broker-dealers | dealer 3  
Receivable from brokers and clearing organizations $ 81,500,000  
Number of customers | customer 2  
Receivable from customers $ 659,700,000  
Number of business days for related transactions (in days) 1 day  
2 Largest Customers | Accounts Receivable | Customer Concentration Risk    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Concentration risk, percentage 43.80%  
Corporate equities    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of securities received as collateral $ 151,500,000 153,300,000
Corporate equities | Reverse Repurchase Agreements    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of collateral 242,200,000 175,800,000
Corporate equities | Securities Borrowed Transactions    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of securities received as collateral, sold and re-pledged under securities loaned 44,800,000 49,100,000
Corporate equities | Repurchase Agreements    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of collateral $ 242,200,000 $ 175,800,000