Segment Operating Results - (Footnotes) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Other Revenue, net	$ 2,660	$ (20,988)
Special Charges, Including Business Realignment Costs	0	23,676
Acquisition and Transition Costs	7	8
Total Other Expenses	7	25,258
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	2,584	(21,592)
Interest expense on Notes Payable	4,570	4,842
Amortization of LP Units and Certain Other Awards	0	1,067
Special Charges, Including Business Realignment Costs	0	23,644
Acquisition and Transition Costs	7	8
Intangible Asset and Other Amortization	0	507
Total Other Expenses	7	25,226
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	76	604
Special Charges, Including Business Realignment Costs	0	32
Acquisition and Transition Costs	0	0
Total Other Expenses	$ 0	$ 32