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, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	$ 786,855	$ 801,494
Trading securities pledged	425,108	686,997
U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	58,992	80,835
U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	101,439	10,594
Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	159,057	267,933
Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	13,366	22,570
Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	245,909	201,579
State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
State and municipal securities		32
Trading securities	130,544	141,274
Securities Owned [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	786,855	801,494
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	58,992	10,594
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	101,439	80,835
Securities Owned [Member] | Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	159,057	267,933
Securities Owned [Member] | Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	13,366	22,570
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed income securities	245,909	201,579
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity securities	77,548	76,709
Securities Owned [Member] | State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
State and municipal securities	130,544	141,274
Securities Sold, But Not yet Purchased [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	587,265	481,214
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	10,029
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	146,592	253,221
Securities Sold, But Not yet Purchased [Member] | Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	28,067	37,201
Securities Sold, But Not yet Purchased [Member] | Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	4,556
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	293,008	100,745
Securities Sold, But Not yet Purchased [Member] | Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity securities	$ 105,013	$ 90,015