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	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	$ 951,854	$ 801,494
Trading securities pledged	847,320	686,997
U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	95,595	80,835
U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	55,172	10,594
Mortgage-backed Securities: Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	194,582	267,933
Mortgage-backed Securities: Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	25,208	22,570
Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	295,825	201,579
Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	121,828	76,709
State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	163,644	141,274
Securities Owned [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	951,854	801,494
Securities Owned [Member] | U.S. Government Agency Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	95,595	80,835
Securities Owned [Member] | U.S. Government Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	55,172	10,594
Securities Owned [Member] | Mortgage-backed Securities: Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	194,582	267,933
Securities Owned [Member] | Mortgage-backed Securities: Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities owned	25,208	22,570
Securities Owned [Member] | Corporate Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed income securities	295,825	201,579
Securities Owned [Member] | Corporate Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity securities	121,828	76,709
Securities Owned [Member] | State And Municipal Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
State and municipal securities	163,644	141,274
Securities Sold, But Not yet Purchased [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities	613,023	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	21,981
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	99,447	253,221
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	97,492	37,201
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	257,458	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	136,581	90,015
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	$ 64	$ 32