Revenues from contracts with customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 218,716
Interest	12,227	$ 10,565
Principal transactions, net	2,726	5,373
Other	861
Total other sources of revenue	15,814
Total revenue	234,530	213,261
Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	72,290
Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,117
Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	77,548
Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,766
Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,444
Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	25,297
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,254
Private Client
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	145,183
Interest	8,837
Principal transactions, net	(80)
Other	154
Total other sources of revenue	8,911
Total revenue	154,094	137,389
Private Client | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	40,278
Private Client | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	10,827
Private Client | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	60,136
Private Client | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,370
Private Client | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Private Client | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	25,297
Private Client | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,275
Asset Management
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	17,639
Interest	5
Principal transactions, net	0
Other	0
Total other sources of revenue	5
Total revenue	17,644	18,666
Asset Management | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Asset Management | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	283
Asset Management | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	17,353
Asset Management | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Asset Management | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Asset Management | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Asset Management | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3
Capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	55,865
Interest	3,205
Principal transactions, net	2,392
Other	67
Total other sources of revenue	5,664
Total revenue	61,529	55,903
Capital markets | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,997
Capital markets | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2
Capital markets | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	51
Capital markets | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,396
Capital markets | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,444
Capital markets | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Capital markets | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(25)
Corporate/Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	29
Interest	180
Principal transactions, net	414
Other	640
Total other sources of revenue	1,234
Total revenue	1,263	$ 1,303
Corporate/Other | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15
Corporate/Other | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5
Corporate/Other | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8
Corporate/Other | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Corporate/Other | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Corporate/Other | Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0
Corporate/Other | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1