Fair Value - Change in fair value option table (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Change in unrealized gain/loss	$ 230,104	$ (442,597)	$ 279,017
Fixed maturities and short term investments [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Change in unrealized gain/loss		(525,787)	186,063
Equities
Fair Value, Option, Quantitative Disclosures [Line Items]
Change in unrealized gain/loss		118,010	66,253
Other invested assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Change in unrealized gain/loss	(2,664)	(6,970)	18,732
Funds Held - Directly Managed [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Change in unrealized gain/loss	$ 1,382	$ (27,850)	$ 7,969