Segment Operating Results - (Footnotes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Other Revenue, net	$ (27,723)	$ 25,315	$ 1,280
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	20,337
Net Loss on Sale and Wind-down of Operations in Mexico, Including Release of Cumulative Foreign Exchange Losses	35,247	0	0
Special Charges, Including Business Realignment Costs	46,645	10,141	5,012
Acquisition and Transition Costs	562	1,013	21
Total Other Expenses	49,457	36,865	30,387
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	(19,845)	19,023	(3,156)
Interest expense on Notes Payable, Subordinated Borrowing and Line of Credit	18,197	12,917	9,201
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	21,070
Amortization of LP Units and Certain Other Awards	1,067	18,183	15,241
Special Charges, Including Business Realignment Costs	46,600	7,202	5,012
Acquisition and Transition Costs	262	705	0
Fair Value Of Contingent Consideration	0	0	1,485
Intangible Asset and Other Amortization	1,183	7,528	8,628
Total Other Expenses	49,112	33,618	30,366
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	(7,878)	6,292	4,436
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	6,295
Net Loss on Sale and Wind-down of Operations in Mexico, Including Release of Cumulative Foreign Exchange Losses	3,441
Special Charges, Including Business Realignment Costs	45	2,939	0
Acquisition and Transition Costs	300	308	21
Total Other Expenses	$ 345	$ 3,247	$ 21