Revenue from contracts with customers - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	$ 37,192	$ 30,816
Total deferred revenue	235	613
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
Revenues	1,394,035	1,198,667	1,033,379
Private Client
Contracts with Customers Assets and Liabilities [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
Revenues	665,060	642,083	653,409
Asset Management
Contracts with Customers Assets and Liabilities [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
Revenues	104,598	130,274	88,755
Capital markets
Contracts with Customers Assets and Liabilities [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
Revenues	625,704	426,752	290,830
Corporate/Other
Contracts with Customers Assets and Liabilities [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)
Revenues	(1,327)	(442)	$ 385
Commissions from sales and trading
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	364,860	359,917
Commissions from sales and trading | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	181,073	174,346
Commissions from sales and trading | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Commissions from sales and trading | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	183,778	185,542
Commissions from sales and trading | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	9	29
Mutual fund income
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	36,747	35,180
Mutual fund income | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	36,651	35,101
Mutual fund income | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	3
Mutual fund income | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	8	9
Mutual fund income | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	88	67
Advisory fees
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	451,197	455,261
Advisory fees | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	346,559	326,858
Advisory fees | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	104,584	128,258
Advisory fees | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	3	2
Advisory fees | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	51	143
Investment banking - capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	240,867	139,763
Investment banking - capital markets | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	24,965	16,093
Investment banking - capital markets | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Investment banking - capital markets | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	215,902	123,670
Investment banking - capital markets | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Investment banking - advisory
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	195,003	82,535
Investment banking - advisory | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	250	0
Investment banking - advisory | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	2,000
Investment banking - advisory | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	194,753	80,535
Investment banking - advisory | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Bank Deposit Sweep Income [Member]
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	15,557	34,829
Bank Deposit Sweep Income [Member] | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	15,557	34,829
Bank Deposit Sweep Income [Member] | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Bank Deposit Sweep Income [Member] | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Bank Deposit Sweep Income [Member] | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	14,638	16,928
Other | Private Client
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	13,382	14,316
Other | Asset Management
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	0	0
Other | Capital markets
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	1,198	2,485
Other | Corporate/Other
Contracts with Customers Assets and Liabilities [Line Items]
Total revenues from contracts with customers	58	127
Investment banking fees
Contracts with Customers Assets and Liabilities [Line Items]
Total deferred revenue	235	613
Commission
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	2,886	3,107
Mutual fund income
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	6,205	5,989
Advisory fees
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	4,546	1,590
Bank Deposit Sweep Income [Member]
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	595	687
Investment banking fees
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	17,765	16,119
Other
Contracts with Customers Assets and Liabilities [Line Items]
Total contract assets	$ 5,195	$ 3,324