Investments (Details 16) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Other Investments [Line Items]
Other invested assets	$ 867,507	$ 1,012,541
Equity Securities [Member]
Other Investments [Line Items]
Other invested assets	98,028	113,900
Limited Partner [Member]
Other Investments [Line Items]
Other invested assets	265,879	251,315
Secured Debt [Member]
Other Investments [Line Items]
Other invested assets	245,246	281,022
Gain (Loss) on Derivatives [Member]
Other Investments [Line Items]
Other invested assets	168,961	257,050
Other [Member]
Other Investments [Line Items]
Other invested assets	$ 89,393	$ 109,254