Derivative Instruments - Earnings relating to derivative instruments not formally designated as hedging instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments Gain Loss [Line Items]
Total derivatives not designated as hedging instruments	$ 30,142	$ 7,301	$ 9,806
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	(256)	497	(4,585)
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	29,886	7,798	5,221
Not Designated as Hedging Instrument | Investment Related Derivatives
Derivative Instruments Gain Loss [Line Items]
Interest rate exposure	15,959	5,065	4,394
Foreign exchange exposure	3,351	(948)	(1,084)
Credit exposure	400	(4,052)	(7,611)
Financial market exposure	411	6,302	3,073
Not Designated as Hedging Instrument | Financial Operations Derivatives
Derivative Instruments Gain Loss [Line Items]
Credit exposure	5,023	(2,437)	10,511
Not Designated as Hedging Instrument | Other Non Investment Derivatives
Derivative Instruments Gain Loss [Line Items]
Contingent capital facility	0	0	0
Guaranteed minimum income benefit contract	2,257	10,457	(2,906)
Modified coinsurance funds withheld contract	2,741	(7,086)	3,429
Life Funds Withheld Assets [Member]
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	$ (488,222)	$ 0	$ 0