Investments (Other Invested Assets) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Other Investments [Line Items]
Other invested assets	$ 1,116,391	$ 1,159,543
Equity securities
Other Investments [Line Items]
Other invested assets	146,910	222,700
Limited partnerships and real estate joint ventures
Other Investments [Line Items]
Other invested assets	417,761	356,419
Structured loans
Other Investments [Line Items]
Other invested assets	245,404	306,497
Derivatives
Other Investments [Line Items]
Other invested assets	87,421	168,208
Other
Other Investments [Line Items]
Other invested assets	$ 218,895	$ 105,719