Business Changes and Developments - Intangible Assets Associated with Acquisitions (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 51,595	$ 51,595
Accumulated Amortization	41,217	32,018
Investment Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	47,320	47,320
Accumulated Amortization	38,523	29,762
Investment Management [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,275	4,275
Accumulated Amortization	2,694	2,256
Client Related [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	45,830	45,830
Accumulated Amortization	37,716	29,332
Client Related [Member] | Investment Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	42,000	42,000
Accumulated Amortization	35,356	27,355
Client Related [Member] | Investment Management [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,830	3,830
Accumulated Amortization	2,360	1,977
Other Intangible Assets Associated With Acquisition [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,765	5,765
Accumulated Amortization	3,501	2,686
Other Intangible Assets Associated With Acquisition [Member] | Investment Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,320	5,320
Accumulated Amortization	3,167	2,407
Other Intangible Assets Associated With Acquisition [Member] | Investment Management [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	445	445
Accumulated Amortization	$ 334	$ 279