Derivative Instruments - Gross amounts of derivative fair values contained in the consolidated balance sheet (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Derivatives Fair Value [Line Items]
Asset derivative fair value		$ 107,496	$ 89,314
Liability derivative fair value		64,704	45,495
Derivative assets - gross amounts offset in the balance sheet	[1]	(17,947)	(3,087)
Derivative liabilities - gross amounts offset in the balance sheet	[1]	(17,947)	(3,087)
Derivative assets - net amounts in the balance sheet	[2]	89,549	86,227
Derivative liabilities - net amounts in the balance sheet	[2]	46,757	42,408
Derivative assets - cash collateral not offset in the balance sheet	[3]	(36,980)	(30,958)
Derivative liabilities - cash collateral not offset in the balance sheet	[3]	(5,810)	0
Derivative assets - net amount		52,569	55,269
Derivative liabilities - net amount		40,947	42,408
Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Asset derivative notional amount		1,396,801	1,667,585
Asset derivative fair value	[2]	85,175	64,289
Liability derivative notional amount		583,722	674,976
Liability derivative fair value	[2]	25,750	11,941
Designated as Hedging Instrument | Foreign Exchange Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount		1,396,801	1,667,585
Asset derivative fair value	[2]	85,175	64,289
Liability derivative notional amount		583,722	674,976
Liability derivative fair value	[2]	25,750	11,941
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Asset derivative notional amount		342,182	441,843
Asset derivative fair value	[2]	22,321	25,025
Liability derivative notional amount		4,472,756	4,909,732
Liability derivative fair value	[2]	38,954	33,554
Not Designated as Hedging Instrument | Investment Related Derivatives | Foreign Exchange Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount		10,049	102,234
Asset derivative fair value	[2]	190	2,888
Liability derivative notional amount		273,767	144,707
Liability derivative fair value	[2]	12,137	1,702
Not Designated as Hedging Instrument | Investment Related Derivatives | Credit Exposure
Derivatives Fair Value [Line Items]
Asset derivative notional amount		32,500	8,433
Asset derivative fair value	[2]	1,077	652
Liability derivative notional amount		82,500	71,614
Liability derivative fair value	[2]	6,978	12,067
Not Designated as Hedging Instrument | Investment Related Derivatives | Financial Market Exposure
Derivatives Fair Value [Line Items]
Asset derivative notional amount		5	37
Asset derivative fair value	[2]	5	77
Liability derivative notional amount		0	26,500
Liability derivative fair value	[2]	0	417
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Foreign Exchange Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount		181,300	194,566
Asset derivative fair value	[2]	1,208	2,009
Liability derivative notional amount		0	0
Liability derivative fair value	[2]	0	0
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Other Credit Derivatives [Member]
Derivatives Fair Value [Line Items]
Asset derivative notional amount		0	29,874
Asset derivative fair value	[2]	0	31
Liability derivative notional amount		24,490	0
Liability derivative fair value	[2]	340	0
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Guaranteed Minimum Income Benefit
Derivatives Fair Value [Line Items]
Asset derivative notional amount		43,553	46,032
Asset derivative fair value	[2]	19,499	19,368
Liability derivative notional amount		43,553	46,032
Liability derivative fair value	[2]	19,499	19,368
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Modified Coinsurance Funds Withheld Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount	[4]	59,775	60,667
Asset derivative fair value	[2],[4]	0	0
Liability derivative notional amount	[4]	4,048,446	4,620,879
Liability derivative fair value	[2],[4]	0	0
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Other Derivative Instruments [Member]
Derivatives Fair Value [Line Items]
Asset derivative notional amount		15,000	0
Asset derivative fair value	[2]	342	0
Liability derivative notional amount		0	0
Liability derivative fair value	[2]	$ 0	$ 0

[1] Other assets and other liabilities include derivative instruments. The derivative balances included in each category are reported on a gross basis by level with a netting adjustment presented separately in the Collateral and Counterparty Netting column. The fair values of the individual derivative contracts are reported gross in their respective levels based on the fair value hierarchy.

[2] 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. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under netting agreements.

[3] As of December 31, 2016, the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015, the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis.

[4] 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. Included in the liability derivative notional amount as of December 31, 2016 is the cumulative net realized and unrealized loss on the life retrocession embedded derivative of $937.7 million.