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	Sep. 30, 2013	Dec. 31, 2012
Trading securities	$ 847,652	$ 763,608
Trading securities pledged	648,111	607,586
U.S. Government Agency Securities [Member]
Trading securities	121,136	123,758
U.S. Government Securities [Member]
Trading securities	13,627	3,573
Corporate Fixed Income Securities [Member]
Trading securities	519,180	396,878
Corporate Equity Securities [Member]
Trading securities	85,183	35,472
State And Municipal Securities [Member]
Trading securities	108,526	203,927
Securities Owned [Member]
Trading securities	847,652	763,608
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Trading securities owned	121,136	123,758
Securities Owned [Member] | U.S. Government Securities [Member]
Trading securities owned	13,627	3,573
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Fixed income securities	519,180	396,878
Securities Owned [Member] | Corporate Equity Securities [Member]
Equity securities	85,183	35,472
Securities Owned [Member] | State And Municipal Securities [Member]
State and municipal securities	108,526	203,927
Securities Sold, But Not yet Purchased [Member]
Trading securities	495,658	319,742
Securities Sold, But Not yet Purchased [Member] | U.S. Government Agency Securities [Member]
Trading securities owned	23,248	15
Securities Sold, But Not yet Purchased [Member] | U.S. Government Securities [Member]
Trading securities owned	174,688	162,661
Securities Sold, But Not yet Purchased [Member] | Corporate Fixed Income Securities [Member]
Fixed income securities	213,757	150,698
Securities Sold, But Not yet Purchased [Member] | Corporate Equity Securities [Member]
Equity securities	83,881	6,281
Securities Sold, But Not yet Purchased [Member] | State And Municipal Securities [Member]
State and municipal securities	$ 84	$ 87