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, 2015	Dec. 31, 2014
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	$ 749,443	$ 786,855
U S Government Corporations And Agencies Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	116,949	101,439
U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	45,167	58,992
Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	203,910	245,909
Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	31,642	77,548
U S States And Political Subdivisions
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	112,983	130,544
Mortgage Backed Securities | Agency Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	205,473	159,057
Mortgage Backed Securities | Non-Agency [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	33,319	13,366
Securities Owned [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	749,443	786,855
Securities Owned [Member] | U S Government Corporations And Agencies Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	45,167	58,992
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	116,949	101,439
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Fixed income securities	203,910	245,909
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Equity securities	31,642	77,548
Securities Owned [Member] | U S States And Political Subdivisions
Schedule Of Trading Securities And Other Trading Assets [Line Items]
State and municipal securities	112,983	130,544
Securities Owned [Member] | Mortgage Backed Securities | Agency Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	205,473	159,057
Securities Owned [Member] | Mortgage Backed Securities | Non-Agency [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	33,319	13,366
Securities Sold, But Not yet Purchased [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments owned, at fair value	521,744	587,265
Securities Sold, But Not yet Purchased [Member] | U S Government Corporations And Agencies Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	186,030	146,592
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		10,029
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	255,700	293,008
Securities Sold, But Not yet Purchased [Member] | Corporate Equity Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Equity securities	29,184	105,013
Securities Sold, But Not yet Purchased [Member] | Mortgage Backed Securities | Agency Securities
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned	$ 50,830	28,067
Securities Sold, But Not yet Purchased [Member] | Mortgage Backed Securities | Non-Agency [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Trading securities owned		$ 4,556