Derivative Instruments - Gross amounts of derivative fair values contained in the consolidated balance sheet (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross amounts recognized in balance sheet		$ 228,475	$ 136,659
Asset derivative fair value		225,236	135,963
Gross amounts recognized in balance sheet		82,884	31,184
Liability derivative fair value		79,645	30,488
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		1,834,298	2,300,609
Gross amounts recognized in balance sheet	[1]	209,675	121,862
Liability derivative notional amount		720,027	302,211
Gross amounts recognized in balance sheet	[1]	52,188	2,936
Derivatives designated as hedging instruments | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		1,834,298	2,300,609
Gross amounts recognized in balance sheet	[1]	209,675	121,862
Liability derivative notional amount		720,027	302,211
Gross amounts recognized in balance sheet	[1]	52,188	2,936
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		599,833	592,791
Gross amounts recognized in balance sheet	[1]	18,800	14,797
Liability derivative notional amount		5,267,561	5,804,625
Gross amounts recognized in balance sheet	[1]	30,696	28,248
Derivatives not designated as hedging instruments | Investment related derivatives | Interest rate exposure
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		10,684	394,597
Gross amounts recognized in balance sheet	[1]	194	206
Liability derivative notional amount		33,934	20,782
Gross amounts recognized in balance sheet	[1]	44	51
Derivatives not designated as hedging instruments | Investment related derivatives | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		301,260	7,385
Gross amounts recognized in balance sheet	[1]	1,628	403
Liability derivative notional amount		139,215	207,182
Gross amounts recognized in balance sheet	[1]	3,786	4,442
Derivatives not designated as hedging instruments | Investment related derivatives | Credit exposure
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		8,963	2,408
Gross amounts recognized in balance sheet	[1]	814	165
Liability derivative notional amount		51,614	14,270
Gross amounts recognized in balance sheet	[1]	12,613	9,836
Derivatives not designated as hedging instruments | Investment related derivatives | Financial market exposure
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		58,875	46,145
Gross amounts recognized in balance sheet	[1]	2,608	360
Liability derivative notional amount		34,794	33,670
Gross amounts recognized in balance sheet	[1]	405	34
Derivatives not designated as hedging instruments | Other non-investment derivatives | Foreign exchange contracts
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		79,101	0
Gross amounts recognized in balance sheet	[1]	164	0
Liability derivative notional amount		8,517	81,194
Gross amounts recognized in balance sheet	[1]	527	282
Derivatives not designated as hedging instruments | Other non-investment derivatives | Other credit derivatives
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		30,281	31,060
Gross amounts recognized in balance sheet		71	60
Liability derivative notional amount		0	0
Gross amounts recognized in balance sheet		0	0
Derivatives not designated as hedging instruments | Other non-investment derivatives | Guaranteed minimum income benefit contract
Derivatives, Fair Value [Line Items]
Asset derivative notional amount		45,006	46,249
Gross amounts recognized in balance sheet	[1]	13,321	13,603
Liability derivative notional amount		45,006	46,249
Gross amounts recognized in balance sheet	[1]	13,321	13,603
Derivatives not designated as hedging instruments | Other non-investment derivatives | Modified coinsurance funds withheld contract
Derivatives, Fair Value [Line Items]
Asset derivative notional amount	[2]	65,663	64,947
Gross amounts recognized in balance sheet	[1],[2]	0	0
Liability derivative notional amount	[2]	4,954,481	5,401,278
Gross amounts recognized in balance sheet	[1],[2]	$ 0	$ 0

[1] Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis.

[2] The fair value movements in derivative assets and liabilities relating to modified coinsurance funds withheld contracts are included within the associated asset or liability at each period end on the face of the balance sheets. Notional amounts associated with reinsurance agreements under which the Company assumes reinsurance risk are recorded as asset derivative notional amounts. Notional amounts associated with the Life Retro Arrangements under which the Company cedes reinsurance risk are recorded as liability derivative notional amounts. Included in the liability derivative notional amount as of June 30, 2015 is the cumulative net realized and unrealized loss on life retrocession embedded derivative of $381.3 million