Schedule IV - Supplementary Reinsurance Information (Details) (Property and casualty, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and casualty
Total premiums earned:
Gross Amount	$ 1,569,021	$ 1,369,017	$ 1,234,204
Ceded to Other Companies	491,448	405,755	365,942
Assumed from Other Companies	760,250	570,504	524,193
Net Amount	$ 1,837,823	$ 1,533,766	$ 1,392,455
Percentage of Amount Assumed to Net	41.00%	37.00%	38.00%

Amount of premiums assumed from other companies.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 2

-Subparagraph (SX 210.12-17)

-URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e574992-122915

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAmountAssumedFromOtherCompanies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of premiums ceded to other companies.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAmountCededToOtherCompanies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Gross amount of premium revenue.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentGrossAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Net amount of gross premiums, less premiums ceded to other companies, plus premiums assumed from other companies; which represents the net amount of premium revenue on the income statement.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentNetAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentNetAmountAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of amount of premiums assumed from other companies to net amount of premiums.

+ References

+ Details

Name:	us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentPercentageOfAmountAssumedToNet
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration