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	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	$ 944,813	$ 786,855
U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	151,895	101,439
U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	29,280	58,992
Mortgage-backed Securities: Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	259,968	159,057
Mortgage-backed Securities: Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	16,377	13,366
Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	270,594	245,909
Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	41,628	77,548
State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	175,071	130,544
Securities Owned [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	944,813	786,855
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	29,280	58,992
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	151,895	101,439
Securities Owned [Member] | Mortgage-backed Securities: Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	259,968	159,057
Securities Owned [Member] | Mortgage-backed Securities: Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	16,377	13,366
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed income securities	270,594	245,909
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity securities	41,628	77,548
Securities Owned [Member] | State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
State and municipal securities	175,071	130,544
Securities Sold, But Not yet Purchased [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Financial instruments owned, at fair value	566,726	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	5,061	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	236,053	146,592
Securities Sold, But Not yet Purchased [Member] | Mortgage-backed Securities: Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	70,715	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	163	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	189,758	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	64,970	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	6
Repurchase Agreements And Short-Term Borrowings [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities pledged	$ 748,100	$ 425,100