Revenue from contracts with customers - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Contract assets (receivables)	$ 47,508	$ 46,187
Deferred revenue (payables)	$ 2,930	$ 930
Commission
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	1 day
Mutual fund and insurance income
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	90 days
Advisory fees
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	90 days
Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	90 days
Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	30 days