Trading Securities Owned And Trading Securities 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	Mar. 31, 2014	Dec. 31, 2013
Trading securities	$ 991,710	$ 801,494
Trading securities pledged	806,676	686,997
U.S. Government Agency Securities [Member]
Trading securities	151,177	88,930
U.S. Government Securities [Member]
Trading securities	23,435	10,594
Corporate Fixed Income Securities [Member]
Trading securities	576,497	483,987
Corporate Equity Securities [Member]
Trading securities	77,181	76,709
State And Municipal Securities [Member]
Trading securities	163,420	141,274
Securities Owned [Member]
Trading securities	991,710	801,494
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Trading securities owned	151,177	88,930
Securities Owned [Member] | U.S. Government Securities [Member]
Trading securities owned	23,435	10,594
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Fixed income securities	576,497	483,987
Securities Owned [Member] | Corporate Equity Securities [Member]
Equity securities	77,181	76,709
Securities Owned [Member] | State And Municipal Securities [Member]
State and municipal securities	163,420	141,274
Securities Sold, But Not yet Purchased [Member]
Trading securities	715,116	481,214
Securities Sold, But Not yet Purchased [Member] | U.S. Government Agency Securities [Member]
Trading securities owned	1,500	2,068
Securities Sold, But Not yet Purchased [Member] | U.S. Government Securities [Member]
Trading securities owned	373,375	253,221
Securities Sold, But Not yet Purchased [Member] | Corporate Fixed Income Securities [Member]
Fixed income securities	224,567	135,878
Securities Sold, But Not yet Purchased [Member] | Corporate Equity Securities [Member]
Equity securities	115,556	90,015
Securities Sold, But Not yet Purchased [Member] | State And Municipal Securities [Member]
State and municipal securities	$ 118	$ 32