Derivative Instruments - Earnings relating to derivative instruments not formally designated as hedging instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments Gain Loss [Line Items]
Total derivatives not designated as hedging instruments	$ 2,521	$ 53,123	$ 30,142
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	0	0	(256)
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	2,521	53,123	29,886
Not Designated as Hedging Instrument | Investment Related Derivatives
Derivative Instruments Gain Loss [Line Items]
Interest rate exposure	781	(2,347)	15,959
Foreign exchange exposure	(592)	(1,542)	3,351
Credit exposure	(1,539)	(2,537)	400
Financial market exposure	(2,494)	(2,190)	411
Not Designated as Hedging Instrument | Financial Operations Derivatives
Derivative Instruments Gain Loss [Line Items]
Credit exposure	0	0	5,023
Not Designated as Hedging Instrument | Other Non Investment Derivatives
Derivative Instruments Gain Loss [Line Items]
Foreign exchange exposure	(1,701)	60,319	0
Credit exposure	4,424	1,375	0
Guaranteed minimum income benefit contract	0	0	2,257
Modified coinsurance funds withheld contract	3,300	45	2,741
Gain Loss On Other Not Designated As Hedging Instruments	342	0	0
Life Funds Withheld Assets
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	$ (540,090)	$ (151,691)	$ (488,222)