Segment Operating Results - (Footnotes) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Other Revenue, net	$ 180	$ 17
Net Realized and Unrealized Gains on Private Equity Fund Investments	346	339
Special Charges	1,897	0
Acquisition and Transition Costs	21	0
Total Other Expenses	8,058	(18,979)
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	(1,428)	(1,178)
Interest expense on Notes Payable, Subordinated Borrowing and Line of Credit	2,261	2,581
Amortization of LP Units / Interests and Certain Other Awards	3,983	(21,371)
Special Charges	1,897	0
Intangible Asset and Other Amortization	2,157	2,392
Total Other Expenses	8,037	(18,979)
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	1,608	1,195
Acquisition and Transition Costs	21	0
Total Other Expenses	$ 21	0
Other Revenue, Including Interest and Investments [Member]
Segment Reporting Information [Line Items]
Principal Trading Losses		(10)
Net Realized and Unrealized Gains on Private Equity Fund Investments		$ 1,064