Collateralized transactions - Schedule of Gross Amounts and Offsetting Amounts of Reverse Repurchase Agreements, Repurchase Agreements, Securities Borrowed and Securities Loaned Transactions (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Reverse repurchase agreements
Gross Amounts of Recognized Assets	$ 193,864	$ 175,765
Gross Amounts Offset on the Balance Sheet	(193,864)	(175,765)
Net Amounts of Assets Presented on the Balance Sheet	0	0
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	0	0
Securities Borrowed
Gross Amounts of Recognized Assets	158,057	160,006
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Assets Presented on the Balance Sheet	158,057	160,006
Financial Instruments	(157,144)	(152,278)
Cash Collateral Received	0	0
Net Amount	913	7,728
Total
Gross Amounts of Recognized Assets	351,921	335,771
Gross Amounts Offset on the Balance Sheet	(193,864)	(175,765)
Net Amounts of Assets Presented on the Balance Sheet	158,057	160,006
Financial Instruments	(157,144)	(152,278)
Cash Collateral Received	0	0
Net Amount	913	7,728
Repurchase agreements
Gross Amounts of Recognized Liabilities	1,162,210	1,172,957
Gross Amounts Offset on the Balance Sheet	(193,864)	(175,765)
Net Amounts of Liabilities Presented on the Balance Sheet	968,346	997,192
Financial Instruments	(968,346)	(997,192)
Cash Collateral Pledged	0	0
Net Amount	0	0
Securities Loaned
Gross Amounts of Recognized Liabilities	320,163	370,331
Gross Amounts Offset on the Balance Sheet	0	0
Net Amounts of Liabilities Presented on the Balance Sheet	320,163	370,331
Financial Instruments	(318,425)	(357,814)
Cash Collateral Pledged	0	0
Net Amount	1,738	12,517
Total
Gross Amounts of Recognized Liabilities	1,482,373	1,543,288
Gross Amounts Offset on the Balance Sheet	(193,864)	(175,765)
Net Amounts of Liabilities Presented on the Balance Sheet	1,288,509	1,367,523
Financial Instruments	(1,286,771)	(1,355,006)
Cash Collateral Pledged	0	0
Net Amount	$ 1,738	$ 12,517