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	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	$ 972,932	$ 1,267,449
U.S. Government Agency Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	66,881	72,532
Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	250,783	310,457
Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	64,009	57,911
State and Municipal Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	137,211	154,622
Loans [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	9,983
U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	9,266	42,121
Sovereign Debt [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	12,403	14,063
Securities Sold, But Not yet Purchased [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	662,852	947,306
Securities Sold, But Not yet Purchased [Member] | U.S. Government Agency Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	1,000	32,755
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	140,100	208,725
Securities Sold, But Not yet Purchased [Member] | Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Equity securities	32,047	36,117
Securities Sold, But Not yet Purchased [Member] | State and Municipal Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
State and municipal securities		7
Securities Sold, But Not yet Purchased [Member] | Loans [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fixed income securities	955
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	243,570	534,817
Securities Sold, But Not yet Purchased [Member] | Mortgage Backed Securities [Member] | Agency [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	231,909	123,456
Securities Sold, But Not yet Purchased [Member] | Sovereign Debt [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Sovereign debt	13,271	11,429
Securities Owned [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Asset-backed securities	28,385	25,905
Financial instruments owned, at fair value	972,932	1,267,449
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	66,881	72,532
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fixed income securities	250,783	310,457
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Equity securities	64,009	57,911
Securities Owned [Member] | State and Municipal Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
State and municipal securities	137,211	154,622
Securities Owned [Member] | Loans [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fixed income securities	9,983
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	9,266	42,121
Securities Owned [Member] | Mortgage Backed Securities [Member] | Agency [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	388,856	564,111
Securities Owned [Member] | Mortgage Backed Securities [Member] | Non-Agency [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	5,155	25,727
Securities Owned [Member] | Sovereign Debt [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Sovereign debt	$ 12,403	$ 14,063