Revenue from contracts with customers - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 1,318,869	$ 1,124,413
Interest	36,482	33,477	$ 50,723
Principal transactions, net	23,984	27,874	30,094
Other	14,700	12,903
Total other sources of revenue	75,166	74,254
Total revenue	1,394,035	1,198,667	1,033,379
Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	364,860	359,917
Mutual fund income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	36,747	35,180
Advisory fees
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	451,197	455,261
Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	240,867	139,763
Investment banking - advisory
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	195,003	82,535
Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	15,557	34,829
Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	14,638	16,928
Private Client
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	618,437	601,543
Interest	29,290	25,148
Principal transactions, net	3,195	3,300
Other	14,138	12,092
Total other sources of revenue	46,623	40,540
Total revenue	665,060	642,083	653,409
Private Client | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	181,073	174,346
Private Client | Mutual fund income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	36,651	35,101
Private Client | Advisory fees
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	346,559	326,858
Private Client | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	24,965	16,093
Private Client | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	250	0
Private Client | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	15,557	34,829
Private Client | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	13,382	14,316
Asset Management
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	104,584	130,261
Interest	0	0
Principal transactions, net	0	0
Other	14	13
Total other sources of revenue	14	13
Total revenue	104,598	130,274	88,755
Asset Management | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Asset Management | Mutual fund income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	3
Asset Management | Advisory fees
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	104,584	128,258
Asset Management | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Asset Management | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	2,000
Asset Management | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Asset Management | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Capital markets
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	595,642	392,243
Interest	6,990	7,749
Principal transactions, net	22,598	26,306
Other	474	454
Total other sources of revenue	30,062	34,509
Total revenue	625,704	426,752	290,830
Capital markets | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	183,778	185,542
Capital markets | Mutual fund income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	8	9
Capital markets | Advisory fees
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	3	2
Capital markets | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	215,902	123,670
Capital markets | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	194,753	80,535
Capital markets | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Capital markets | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	1,198	2,485
Corporate/Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	206	366
Interest	202	580
Principal transactions, net	(1,809)	(1,732)
Other	74	344
Total other sources of revenue	(1,533)	(808)
Total revenue	(1,327)	(442)	$ 385
Corporate/Other | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	9	29
Corporate/Other | Mutual fund income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	88	67
Corporate/Other | Advisory fees
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	51	143
Corporate/Other | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Corporate/Other | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Corporate/Other | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	0	0
Corporate/Other | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers	$ 58	$ 127