Fair value measurements - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Assets
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Principal transactions, net
Auction rate securities
Assets
Beginning Balance	$ 2,713	$ 31,776
Total Realized and Unrealized Losses	9	3,159
Purchases and Issuances	0	0
Sales and Settlements	(70)	(32,222)
Transfers In / (Out)	0	0
Ending Balance	2,652	2,713
Trade claims
Assets
Beginning Balance	0
Total Realized and Unrealized Losses	0
Purchases and Issuances	1,427
Sales and Settlements	0
Transfers In / (Out)	1,257
Ending Balance	$ 2,684	$ 0