Revenues from contracts with customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 231,024	$ 220,720	$ 449,945	$ 439,436
Interest	13,550	13,056	26,277	25,283
Principal transactions, net	3,045	6,400	14,483	9,126
Other	3,316	2,380	12,000	3,241
Total other sources of revenue	19,911	21,836	52,760	37,650
Total revenue	250,935	242,556	502,705	477,086
Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	70,766	72,177	140,561	144,467
Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,130	10,673	19,744	21,790
Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	80,707	77,270	154,354	154,818
Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,961	19,665	30,303	38,431
Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,045	8,239	29,746	17,683
Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,830	28,853	65,798	54,150
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,585	3,843	9,439	8,097
Private Client
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	148,848	145,060	292,978	290,243
Interest	9,639	9,514	19,047	18,351
Principal transactions, net	538	212	2,222	132
Other	2,903	1,767	11,208	1,921
Total other sources of revenue	13,080	11,493	32,477	20,404
Total revenue	161,928	156,553	325,455	310,647
Private Client | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,026	39,093	74,502	79,371
Private Client | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,124	10,441	19,738	21,268
Private Client | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	62,080	59,774	119,124	119,910
Private Client | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,262	3,469	7,011	7,839
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	31,830	28,853	65,798	54,150
Private Client | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,526	3,430	6,805	7,705
Asset Management
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,618	17,710	35,201	35,349
Interest	0	(4)	0	1
Principal transactions, net	0	0	0	0
Other	4	0	7	0
Total other sources of revenue	4	(4)	7	1
Total revenue	18,622	17,706	35,208	35,350
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	1	222	(5)	505
Asset Management | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,617	17,485	35,206	34,838
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	0	3	0	6
Capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	62,005	57,922	119,940	113,787
Interest	3,459	3,263	6,294	6,468
Principal transactions, net	6,312	6,989	16,469	9,381
Other	43	32	77	99
Total other sources of revenue	9,814	10,284	22,840	15,948
Total revenue	71,819	68,206	142,780	129,735
Capital markets | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	33,736	33,022	66,052	65,019
Capital markets | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1	5	2	7
Capital markets | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2	3	7	54
Capital markets | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,699	16,196	23,292	30,592
Capital markets | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	13,045	8,239	29,746	17,683
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	522	457	841	432
Corporate/Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,553	28	1,826	57
Interest	452	283	936	463
Principal transactions, net	(3,805)	(801)	(4,208)	(387)
Other	366	581	708	1,221
Total other sources of revenue	(2,987)	63	(2,564)	1,297
Total revenue	(1,434)	91	(738)	1,354
Corporate/Other | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4	62	7	77
Corporate/Other | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4	5	9	10
Corporate/Other | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8	8	17	16
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	$ 1,537	$ (47)	$ 1,793	$ (46)