Investments (Details 8) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2011	Dec. 31, 2010
Securities Financing Transaction [Line Items]
Securities lending collateral	$ 21,409	$ 22,328
Percentage of total	100.00%	100.00%
AAA [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	173	5,454
Percentage of total	0.80%	24.40%
AA+ [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	0	11,003
Percentage of total	0.00%	49.30%
AA [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	0	0
Percentage of total	0.00%	0.00%
AA- [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	0	2,998
Percentage of total	0.00%	13.50%
A+ [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	0	0
Percentage of total	0.00%	0.00%
A [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	0	0
Percentage of total	0.00%	0.00%
NR [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	257	229
Percentage of total	1.20%	1.00%
Short-term investments [Member] \| NR [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	20,979	2,644
Percentage of total	98.00%	11.80%
Short-term investments [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	21,152	17,094
Rated Securities [Member]
Securities Financing Transaction [Line Items]
Securities lending collateral	$ 430	$ 19,684
Percentage of total	2.00%	88.20%

The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Chapter 4
-Paragraph 49
-IssueDate 2006-05-01
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 10
-Section 05
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=6901665&loc=d3e93645-111703

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 17
-Subparagraph a(3)
-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 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6862952&loc=d3e113969-111729

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 15
-Subparagraph a, b, c, d
-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 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 91
-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