Revenue from contracts with customers - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	$ 34,680	$ 32,773
Deferred revenue (payables)	1,803	900
Investment banking fees
Capitalized Contract Cost [Line Items]
Deferred revenue (payables)	1,120	900
IRA fees
Capitalized Contract Cost [Line Items]
Deferred revenue (payables)	683	0
Commission
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	3,428	3,533
Mutual fund income
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	5,472	4,993
Advisory fees
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	3,602	5,368
Bank deposit sweep income
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	5,173	9,057
Investment banking fees
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	9,775	5,136
Other
Capitalized Contract Cost [Line Items]
Contract assets (receivables)	$ 7,230	$ 4,686