Revenues from contracts with customers (Contract Assets and Liabilities) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Capitalized Contract Cost [Line Items]
Contract assets	$ 22,676,000	$ 28,888,000
Deferred income, IRA fees	2,195,000	408,000
Commission
Capitalized Contract Cost [Line Items]
Contract assets	4,298,000	2,824,000
Mutual Fund Income
Capitalized Contract Cost [Line Items]
Contract assets	6,736,000	6,746,000
Advisory fees
Capitalized Contract Cost [Line Items]
Contract assets	1,080,000	1,594,000
Bank Deposit Sweep Income
Capitalized Contract Cost [Line Items]
Contract assets	1,610,000	3,454,000
Investment Banking Fees
Capitalized Contract Cost [Line Items]
Contract assets	4,392,000	9,284,000
Other Income [Member]
Capitalized Contract Cost [Line Items]
Contract assets	4,560,000	4,986,000
Investment Banking Fees
Capitalized Contract Cost [Line Items]
Deferred income, IRA fees	289,000	408,000
IRA fees (7)
Capitalized Contract Cost [Line Items]
Deferred income, IRA fees	$ 1,906,000	$ 0