Derivative Instruments - Net Realized and unrealized gains (losses) on derivative instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	$ (906)	$ 906	$ (7,975)	$ (2,716)
Derivatives not designated as hedging instruments | Investment related derivatives
Derivative [Line Items]
Interest rate exposure	372	0	158	781
Foreign currency exposure	(988)	4	(1,733)	(666)
Credit exposure	(525)	16	(1,379)	(147)
Financial market exposure	0	(1,811)	185	(2,821)
Derivatives not designated as hedging instruments | Other non-investment derivatives
Derivative [Line Items]
Foreign currency exposure	34	183	(1,176)	(998)
Credit exposure	138	250	770	(53)
Gain Loss On Guaranteed Minimum Income Benefit Contract Not Designated As Hedging Instruments	0	0	0	0
Modified coinsurance funds withheld contract, including life retrocession embedded derivative	238	2,264	(3,687)	1,188
Gain Loss On Other Not Designated As Hedging Instruments	(175)	0	(1,113)	0
Life Funds Withheld Assets
Derivative [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	$ (34,596)	$ (229,742)	$ (84,697)	$ (465,822)