Significant Accounting Policies All Other - Revenue From Contract With Customers (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 257,484	$ 182,317
Management Fees	11,604	7,141
Incentive income	0	15
Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	257,226	181,804
Management Fees	11,346	6,643
Incentive income	0	0
Asset Company
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	258	513
Management Fees	258	498
Incentive income	0	15
Underwriting fees | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	63,270	48,036
Strategic/financial advisory fees | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	21,996	20,544
Placement and sales agent fees | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	17,596	9,498
Expense reimbursements from clients | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,166	2,028
Investment banking revenue | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	105,028	80,106
Brokerage | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	140,852	95,055
Commissions | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	132,208	87,359
Trade conversion | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,639	4,106
Equity and credit research fees | Operating Company [Member]
Organization [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 4,005	$ 3,590