Investments (Details 19) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Other Investments [Abstract]
Other invested assets	$ 1,159,543,000	$ 1,012,541,000
Equity Securities [Member]
Other Investments [Abstract]
Other invested assets	222,700,000	113,900,000
Limited Partner [Member]
Other Investments [Abstract]
Other invested assets	356,419,000	251,315,000
Secured Debt [Member]
Other Investments [Abstract]
Other invested assets	306,497,000	281,022,000
Gain (Loss) on Derivatives [Member]
Other Investments [Abstract]
Other invested assets	168,208,000	257,050,000
Other [Member]
Other Investments [Abstract]
Other invested assets	$ 105,719,000	$ 109,254,000

Other investments not otherwise specified in the taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(f,g))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 1

-Subparagraph g

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant