Revenues from contracts with customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 214,528	$ 220,228	$ 664,473	$ 659,664
Interest	12,344	13,403	38,621	38,686
Principal transactions, net	7,606	(16)	22,089	9,110
Other	315	4,199	12,315	7,440
Total other sources of revenue	20,265	17,586	73,025	55,236
Total revenue	234,793	237,814	737,498	714,900
Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	68,572	68,370	209,133	212,837
Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,055	11,308	29,799	33,098
Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	80,887	78,154	235,241	232,972
Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,330	18,539	41,633	56,970
Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,468	9,789	40,214	27,472
Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	28,894	30,053	94,692	84,203
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,322	4,015	13,761	12,112
Private Client
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	143,301	144,568	436,279	434,811
Interest	8,652	9,469	27,699	27,820
Principal transactions, net	70	675	2,292	807
Other	31	3,371	11,239	5,292
Total other sources of revenue	8,753	13,515	41,230	33,919
Total revenue	152,054	158,083	477,509	468,730
Private Client | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	35,994	36,553	110,496	115,924
Private Client | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,050	11,059	29,788	32,327
Private Client | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	62,510	60,516	181,634	180,426
Private Client | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,557	2,733	9,568	10,572
Private Client | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Private Client | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	28,894	30,053	94,692	84,203
Private Client | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,296	3,654	10,101	11,359
Asset Management
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,368	17,870	53,569	53,219
Interest	0	0	0	1
Principal transactions, net	0	0	0	0
Other	0	0	7	0
Total other sources of revenue	0	0	7	1
Total revenue	18,368	17,870	53,576	53,220
Asset Management | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Asset Management | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	240	(5)	745
Asset Management | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,366	17,627	53,572	52,465
Asset Management | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Asset Management | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Asset Management | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Asset Management | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2	3	2	9
Capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	52,261	57,727	172,201	171,514
Interest	3,272	3,678	9,566	10,146
Principal transactions, net	8,515	6,423	24,984	15,804
Other	20	302	97	401
Total other sources of revenue	11,807	10,403	34,647	26,351
Total revenue	64,068	68,130	206,848	197,865
Capital markets | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	32,569	31,807	98,621	96,826
Capital markets | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1	4	3	11
Capital markets | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2	3	9	57
Capital markets | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,773	15,806	32,065	46,398
Capital markets | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,468	9,789	40,214	27,472
Capital markets | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Capital markets | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	448	318	1,289	750
Corporate/Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	598	63	2,424	120
Interest	420	256	1,356	719
Principal transactions, net	(979)	(7,114)	(5,187)	(7,501)
Other	264	526	972	1,747
Total other sources of revenue	(295)	(6,332)	(2,859)	(5,035)
Total revenue	303	(6,269)	(435)	(4,915)
Corporate/Other | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9	10	16	87
Corporate/Other | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4	5	13	15
Corporate/Other | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9	8	26	24
Corporate/Other | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate/Other | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate/Other | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Corporate/Other | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 576	$ 40	$ 2,369	$ (6)