Revenues from contracts with customers (Contract Assets and Liabilities) (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Capitalized Contract Cost [Line Items]
Contract assets	$ 29,869,000	$ 28,888,000
Deferred income, IRA fees	1,929,000	408,000
Commission
Capitalized Contract Cost [Line Items]
Contract assets	3,519,000	2,824,000
Mutual Fund Income
Capitalized Contract Cost [Line Items]
Contract assets	6,168,000	6,746,000
Advisory fees
Capitalized Contract Cost [Line Items]
Contract assets	1,129,000	1,594,000
Bank Deposit Sweep Income
Capitalized Contract Cost [Line Items]
Contract assets	790,000	3,454,000
Investment Banking Fees
Capitalized Contract Cost [Line Items]
Contract assets	13,592,000	9,284,000
Other Income [Member]
Capitalized Contract Cost [Line Items]
Contract assets	4,671,000	4,986,000
Investment Banking Fees
Capitalized Contract Cost [Line Items]
Deferred income, IRA fees	659,000	408,000
IRA fees (7)
Capitalized Contract Cost [Line Items]
Deferred income, IRA fees	$ 1,270,000	$ 0