Revenues from contracts with customers (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 218,920
Interest	12,727	$ 12,227
Principal transactions, net	11,438	2,726
Other	8,685
Total other sources of revenue	32,850
Total revenue	251,770	234,530
Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	69,795
Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,614
Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	73,647
Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,342
Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,701
Bank deposit sweep income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	33,968
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,853
Private Client
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	144,130
Interest	9,408
Principal transactions, net	1,684
Other	8,305
Total other sources of revenue	19,397
Total revenue	163,527	154,094
Private Client | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,477
Private Client | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,614
Private Client | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57,044
Private Client | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,749
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	33,968
Private Client | Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,278
Asset Management
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,583
Interest	0
Principal transactions, net	0
Other	3
Total other sources of revenue	3
Total revenue	16,586	17,644
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	(6)
Asset Management | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,589
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	0
Capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57,935
Interest	2,835
Principal transactions, net	10,157
Other	34
Total other sources of revenue	13,026
Total revenue	70,961	$ 61,529
Capital markets | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	32,316
Capital markets | Mutual fund income
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1
Capital markets | Advisory fees
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5
Capital markets | Investment banking - capital markets
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	8,593
Capital markets | Investment banking - advisory
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,701
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	319
Corporate/Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	272
Interest	484
Principal transactions, net	(403)
Other	343
Total other sources of revenue	424
Total revenue	696
Corporate/Other | Commissions from sales and trading
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2
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	9
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	$ 256