Reinsurance (Details) - Ceded Credit Risk	Dec. 31, 2012
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	100.00%
Threshold percentage, concentration risk	3.00%
AAA
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	1.20%
AA
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	53.10%
AA- | Munich Reinsurance Company
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	25.40%
AA- | Swiss Reinsurance Company
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	11.00%
AA- | Swiss Re Europe S.A.
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	5.50%
A+ | Transatlantic Reinsurance Company
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	4.00%
A+ | LLoyds Syndicate [Member]
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	8.00%
A
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	37.10%
A- or better rating
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	91.00%
BBB
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	0.30%
BB and below
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	0.00%
Captives
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	6.10%
Other
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	2.00%
Not Rated
Ceded Credit Risk [Line Items]
Percentage of total reinsurance recoverables	0.20%