Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Investment Banking And Investment Management Receivables Collection Periods		90 days
Placement Fees Receivables Collection Period		180 days
Private Funds Capital Raising Receivables Collection Period		1 year
Collection Period For Restructuring Transactions And Private Equity Fee Receivables		90 days
Receivables Reflected in Other Assets in Excess of Period		1 year
Contract Asset Recognized in Benefit in Excess of Period		1 year
Other Operating Expenses(1)	[1]	$ 7,270	$ 5,591
Professional Fees	[1]	16,050	16,745
Net Realized and Unrealized Gains on Private Equity Fund Investments		346	339
Variable Interest Entity, Primary Beneficiary [Member]
Significant Accounting Policies [Line Items]
Consolidated Assets		67,262		$ 126,078
Consolidated Liabilities		$ 54,059		$ 102,487
Execution, Clearing and Custody Fees [Member]
Significant Accounting Policies [Line Items]
Other Operating Expenses(1)			3,526
Professional Fees			333
Other Revenue, Including Interest and Investments [Member]
Significant Accounting Policies [Line Items]
Principal Trading Losses			(10)
Net Realized and Unrealized Gains on Private Equity Fund Investments			$ 1,064

[1] Certain balances in the prior period were reclassified to conform to their current presentation. See Note 2 for further information.