Revenue from contracts with customers - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Contract with customer, receivables	$ 39,861,000	$ 32,773,000
Contract assets	0	0
Total deferred revenue	1,118,000	900,000
Capitalized contract costs	$ 1,900,000	$ 1,400,000
Commission From Equity Securities Transactions
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	2 days
Commissions From Corporate Bond Transactions
Disaggregation of Revenue [Line Items]
Revenue settlement period (in days)	1 day
Mutual fund 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