Significant Accounting Policies (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019
Significant Accounting Policies [Line Items]
Assets		$ 2,645,458		$ 2,598,613	$ 2,211,103
Liabilities		$ 1,438,444		1,472,363
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		$ 1,310
Investment Banking And Investment Management Receivables Collection Periods		90 days
Placement Fees Receivables Collection Period		180 days
Collection Period For Restructuring Transactions		90 days
Contract Asset Recognized For Cost of Obtaining Contract With Benefit in Excess of Period		1 year
Retained Earnings [Member]
Significant Accounting Policies [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]		$ 1,310
Variable Interest Entity, Primary Beneficiary [Member]
Significant Accounting Policies [Line Items]
Assets		$ 228,884		227,885
Liabilities		$ 102,217		$ 129,494

[1] (1) The cumulative adjustment relates to the adoption of Accounting Standards Update ("ASU") No. 2016-13, "Measurement of Credit Losses on Financial Instruments" ("ASU 2016-13") on January 1, 2020, for which the Company recorded an adjustment to Retained Earnings to reflect the increase in the Company's Allowance for Doubtful Accounts as a result of the use of the current expected credit loss model. See Notes 2 and 3 for further information.