Fair Value Of Financial Instruments (Schedule Of Valuation Of Financial Instruments By Pricing Observability Levels) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Cash and cash equivalents	$ 78,163	$ 72,596
Trading securities owned, at fair value	801,494	763,608
Available-for-sale securities, Estimated fair value	1,756,253	1,625,168
Investments	217,228	236,434
Total Assets	2,853,138	2,697,806
Trading securities sold, but not yet purchased, at fair value	481,214	342,708
Derivative contracts, Liabilities	9,349	19,934
Total Liabilities	490,563	362,642
Level 1 [Member]
Cash and cash equivalents	78,163	72,596
Trading securities owned, at fair value	110,469	104,018
Available-for-sale securities, Estimated fair value	83,655	263,017
Investments	49,406	58,872
Total Assets	321,693	498,503
Trading securities sold, but not yet purchased, at fair value	358,011	237,837
Total Liabilities	358,011	237,837
Level 2 [Member]
Trading securities owned, at fair value	688,745	659,007
Available-for-sale securities, Estimated fair value	1,608,320	1,271,664
Investments	2,422	61,801
Total Assets	2,299,487	1,992,472
Trading securities sold, but not yet purchased, at fair value	123,203	104,871
Derivative contracts, Liabilities	9,349	19,934
Total Liabilities	132,552	124,805
Level 3 [Member]
Trading securities owned, at fair value	2,280	583
Available-for-sale securities, Estimated fair value	64,278	90,487
Investments	165,400	115,761
Total Assets	231,958	206,831
U.S. Government Agency Securities [Member]
Trading securities owned, at fair value	88,930	123,758
Available-for-sale securities, Estimated fair value	1,072	1,113
Trading securities sold, but not yet purchased, at fair value	2,068	15
U.S. Government Agency Securities [Member] | Level 2 [Member]
Trading securities owned, at fair value	88,930	123,758
Available-for-sale securities, Estimated fair value	1,072	1,113
Trading securities sold, but not yet purchased, at fair value	2,068	15
U.S. Government Securities [Member]
Trading securities owned, at fair value	10,594	3,573
Investments		7,069
Trading securities sold, but not yet purchased, at fair value	253,221	162,661
U.S. Government Securities [Member] | Level 1 [Member]
Trading securities owned, at fair value	10,594	3,573
Investments		7,069
Trading securities sold, but not yet purchased, at fair value	253,221	162,661
Corporate Fixed Income Securities [Member]
Trading securities owned, at fair value	483,987	396,878
Available-for-sale securities, Estimated fair value	498,316	480,182
Trading securities sold, but not yet purchased, at fair value	135,878	150,698
Corporate Fixed Income Securities [Member] | Level 1 [Member]
Trading securities owned, at fair value	23,413	66,795
Available-for-sale securities, Estimated fair value	83,655	263,017
Trading securities sold, but not yet purchased, at fair value	17,857	46,274
Corporate Fixed Income Securities [Member] | Level 2 [Member]
Trading securities owned, at fair value	458,535	329,500
Available-for-sale securities, Estimated fair value	414,661	217,165
Trading securities sold, but not yet purchased, at fair value	118,021	104,424
Corporate Fixed Income Securities [Member] | Level 3 [Member]
Trading securities owned, at fair value	2,039	583
Corporate Equity Securities [Member]
Trading securities owned, at fair value	76,709	35,472
Investments	32,402	32,162
Trading securities sold, but not yet purchased, at fair value	90,015	29,247
Corporate Equity Securities [Member] | Level 1 [Member]
Trading securities owned, at fair value	76,462	33,650
Investments	32,402	32,162
Trading securities sold, but not yet purchased, at fair value	86,933	28,902
Corporate Equity Securities [Member] | Level 2 [Member]
Trading securities owned, at fair value	6	1,822
Trading securities sold, but not yet purchased, at fair value	3,082	345
Corporate Equity Securities [Member] | Level 3 [Member]
Trading securities owned, at fair value	241
Corporate Preferred Securities [Member]
Investments		56,970
Corporate Preferred Securities [Member] | Level 2 [Member]
Investments		56,970
State And Municipal Securities [Member]
Trading securities owned, at fair value	141,274	203,927
Available-for-sale securities, Estimated fair value	90,677	157,420
Trading securities sold, but not yet purchased, at fair value	32	87
State And Municipal Securities [Member] | Level 2 [Member]
Trading securities owned, at fair value	141,274	203,927
Available-for-sale securities, Estimated fair value	84,477	66,933
Trading securities sold, but not yet purchased, at fair value	32	87
State And Municipal Securities [Member] | Level 3 [Member]
Available-for-sale securities, Estimated fair value	6,200	90,487
Agency [Member]
Available-for-sale securities, Estimated fair value	183,987	684,848
Agency [Member] | Level 2 [Member]
Available-for-sale securities, Estimated fair value	183,987	684,848
Commercial [Member]
Available-for-sale securities, Estimated fair value	211,246	260,974
Commercial [Member] | Level 2 [Member]
Available-for-sale securities, Estimated fair value	211,246	260,974
Non-Agency [Member]
Available-for-sale securities, Estimated fair value	4,619	13,878
Non-Agency [Member] | Level 2 [Member]
Available-for-sale securities, Estimated fair value	4,619	13,878
Asset-Backed Securities [Member]
Available-for-sale securities, Estimated fair value	766,336	26,753
Asset-Backed Securities [Member] | Level 2 [Member]
Available-for-sale securities, Estimated fair value	708,258	26,753
Asset-Backed Securities [Member] | Level 3 [Member]
Available-for-sale securities, Estimated fair value	58,078
Mutual Funds [Member]
Investments	16,994	18,021
Mutual Funds [Member] | Level 1 [Member]
Investments	16,994	18,021
Auction Rate Equity Securities [Member]
Investments	56,693	64,397
Auction Rate Equity Securities [Member] | Level 3 [Member]
Investments	56,693	64,397
Auction Rate Municipal Securities [Member]
Investments	10,939	14,067
Auction Rate Municipal Securities [Member] | Level 3 [Member]
Investments	10,939	14,067
Other Investment [Member]
Investments	100,200	43,748
Other Investment [Member] | Level 1 [Member]
Investments	10	1,620
Other Investment [Member] | Level 2 [Member]
Investments	2,422	4,831
Other Investment [Member] | Level 3 [Member]
Investments	$ 97,768	$ 37,297