Derivative Instruments - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Derivative [Line Items]
Derivative assets - cash collateral not offset in the balance sheet		$ 30,958		$ 78,580
Collateral posted to counterparty		0		0
Net results from structured products		17,991	[1]	54,209	[2]	$ 23,791	[3]
Asset derivative fair value		89,314		136,659
Net realized and unrealized gains (losses) on derivative instruments		53,123		29,886		7,798
Fair Value Hedging Member | Deposit Liabilities
Derivative [Line Items]
Fair Value Hedge Remaining Balance		129,454		137,862
Fair Value Hedging Member | Structured Indemnity | Deposit Liabilities
Derivative [Line Items]
Fair Value Hedge Remaining Balance				47,000
Life Funds Withheld Assets [Member]
Derivative [Line Items]
Cumulative net realized and unrealized gains (losses) on life retrocession embedded derivative		(463,900)
Net realized and unrealized gains (losses) on derivative instruments		(151,691)		(488,222)		0
Not Designated as Hedging Instrument
Derivative [Line Items]
Asset derivative notional amount		441,843		592,791
Asset derivative fair value	[4]	25,025		14,797
Other Non Investment Derivatives | Not Designated as Hedging Instrument | Other Credit Derivatives [Member]
Derivative [Line Items]
Asset derivative notional amount		29,874		31,060
Asset derivative fair value	[4]	31		60
Net realized and unrealized gains (losses) on derivative instruments	[4]	100
Interest expense | Structured Indemnity
Derivative [Line Items]
Net results from structured products				28,700
Interest expense | Property and casualty operations
Derivative [Line Items]
Net results from structured products		$ (42,200)		$ (12,900)		$ (48,000)

[1] The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.

[2] The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million, respectively.

[3] The net results from P&C structured products include net investment income and interest expense of $71.9 million and $48.0 million, respectively.

[4] 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.