Derivative Instruments - Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Derivative [Line Items]
Cumulative net realized and unrealized loss on life retrocession embedded derivative	$ (654,600,000)
Gross amounts recognized in balance sheet	257,880,000				136,659,000
Net realized and unrealized gains (losses) on derivative instruments	16,521,000		1,810,000
Gross amounts not offset in the balance sheet - cash collateral	183,675,000				78,580,000
Net results from structured products	5,025,000	[1]	7,953,000	[2]
Fair value hedges | Deposit liabilities
Derivative [Line Items]
Remaining balance	135,490,000		191,925,000
Structured Indemnity [Member] | Fair value hedges | Deposit liabilities
Derivative [Line Items]
Remaining balance	47,000,000
Structured Indemnity [Member] | Interest expense
Derivative [Line Items]
Net results from structured products	28,700,000
Derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative Asset, Notional Amount	2,770,578,000				592,791,000
Gross amounts recognized in balance sheet	219,504,000	[3]			14,797,000	[3]
Other non-investment derivatives | Derivatives not designated as hedging instruments | Other Credit Derivatives [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	31,060,000				31,060,000
Gross amounts recognized in balance sheet	218,000				60,000
Net realized and unrealized gains (losses) on derivative instruments	$ 100,000

[1] The net results from P&C structured products include net investment income and interest expense of $15.1 million and $10.0 million, respectively.

[2] The net results from P&C structured products include net investment income and interest expense of $18.8 million and $10.8 million, respectively.

[3] 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.