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	Sep. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	$ 812,976	$ 786,855
Trading securities pledged	388,500
U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	124,292	101,439
U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	15,750	58,992
Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	251,416	245,909
Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	25,641	77,548
State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	174,693	130,544
Mortgage-backed securities [Member] | Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	202,480	159,057
Mortgage-backed securities [Member] | Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	18,704	13,366
Securities Owned [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	812,976	786,855
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	15,750	58,992
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	124,292	101,439
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed income securities	251,416	245,909
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity securities	25,641	77,548
Securities Owned [Member] | State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
State and municipal securities	174,693	130,544
Securities Owned [Member] | Mortgage-backed securities [Member] | Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	202,480	159,057
Securities Owned [Member] | Mortgage-backed securities [Member] | Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	18,704	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	512,323	587,265
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	217,648	146,592
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	234,429	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	21,089	105,013
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	230
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	38,927	28,067
Securities Sold, But Not yet Purchased [Member] | Mortgage-backed securities [Member] | Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned		4,556
Repurchase Agreements And Short-Term Borrowings [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities pledged	$ 748,100	$ 425,100