Financial Instruments Owned And Financial Instruments Sold, But Not Yet Purchased (Components Of Trading Securities Owned And Trading Securities Sold, But Not Yet Purchased) (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		$ 981,282	$ 694,028
U.S. Government Agency Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		166,501	56,450
Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		223,545	194,575
Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		82,402	67,593
State and Municipal Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		162,083	96,150
U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		61,918	46,900
Securities Sold, But Not yet Purchased [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value		644,762	437,978
Other	[1]	15,123	11,303
Securities Sold, But Not yet Purchased [Member] | Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fixed income securities		185,728	162,626
Securities Sold, But Not yet Purchased [Member] | Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Equity securities		34,443	30,848
Securities Sold, But Not yet Purchased [Member] | U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned		287,820	91,974
Securities Sold, But Not yet Purchased [Member] | Agency Mortgage-Backed Securities [Member] | Agency Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned		121,648	141,227
Securities Owned [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Other	[2]	30,630	15,926
Financial instruments owned, at fair value		981,282	694,028
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned		166,501	56,450
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fixed income securities		223,545	194,575
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Equity securities		82,402	67,593
Securities Owned [Member] | State and Municipal Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
State and municipal securities		162,083	96,150
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned		61,918	46,900
Securities Owned [Member] | Agency Mortgage-Backed Securities [Member] | Agency Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned		$ 254,203	$ 216,434

[1] Includes U.S. government agency securities, sovereign debt, and state and municipal securities.

[2] Includes loans, asset-backed securities, sovereign debt, and non-agency mortgage-backed securities.