Investments (Details 19) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Other Investments [Line Items]
Other invested assets	$ 1,129,651,000	$ 1,159,543,000
Equity Securities [Member]
Other Investments [Line Items]
Other invested assets	220,665,000	222,700,000
Limited Partner [Member]
Other Investments [Line Items]
Other invested assets	375,451,000	356,419,000
Secured Debt [Member]
Other Investments [Line Items]
Other invested assets	272,592,000	306,497,000
Gain (Loss) on Derivatives [Member]
Other Investments [Line Items]
Other invested assets	151,761,000	168,208,000
Other [Member]
Other Investments [Line Items]
Other invested assets	$ 109,182,000	$ 105,719,000