Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	$ 84,119	$ 99,613
U.S. government agency MBS [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	47	16
U.S. Treasury securities [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	10,811	11,755
Corporate bonds and redeemable preferred stock [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	64,651	87,537
Foreign government bonds [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	23	158
Municipal bonds [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	122	143
Exchange traded funds [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	1,636
Certificates of deposit [Member]
Trading securities sold, not yet purchased
Trading securities sold, not yet purchased	$ 6,829	$ 4

Fair value of obligations incurred from short sales.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 38

-IssueDate 2006-05-01

-Chapter 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 19

-IssueDate 2006-05-01

-Chapter 7

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 35

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6475908&loc=d3e42429-110968

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 2

-IssueDate 2006-05-01

-Chapter 7

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 40

-IssueDate 2006-05-01

-Chapter 7

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details