Derivative Instruments - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Derivative assets - cash collateral not offset in the balance sheet	$ 78,580,000		$ 0
Collateral posted to counterparty	0		19,847,000
Net results from structured products	54,209,000		23,791,000		5,257,000
Asset derivative fair value	136,659,000		27,487,000
Net realized and unrealized gains (losses) on derivative instruments	29,886,000		7,798,000		5,221,000
Deposit Liabilities
Derivative [Line Items]
Periodic coupon settlement decrease to interest expense	0		0		4,900,000
Credit Risk Contract
Derivative [Line Items]
Number of instruments held	1
Deficiency guarantee from German state and federal governments (percentage)	68.00%
Property and casualty operations | Interest Expense [Member]
Derivative [Line Items]
Net results from structured products	(12,900,000)		(48,000,000)		(66,300,000)
Property and casualty operations | Interest Expense [Member] | Structured Indemnity
Derivative [Line Items]
Net results from structured products	28,700,000
Fair Value Hedging Member | Deposit Liabilities
Derivative [Line Items]
Fair Value Hedge Remaining Balance	137,862,000		195,814,000
Fair Value Hedging Member | Structured Indemnity | Deposit Liabilities
Derivative [Line Items]
Fair Value Hedge Remaining Balance	47,000,000
Life Funds Withheld Assets [Member]
Derivative [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative	(450,831,000)
Net realized and unrealized gains (losses) on derivative instruments	(488,222,000)		0		0
Not Designated as Hedging Instrument
Derivative [Line Items]
Asset derivative notional amount	592,791,000		172,800,000
Asset derivative fair value	14,797,000	[1]	1,389,000	[1]
Other Non Investment Derivatives | Not Designated as Hedging Instrument | Other Credit Derivatives [Member]
Derivative [Line Items]
Asset derivative notional amount	31,060,000	[2]	0	[2]
Asset derivative fair value	60,000	[1],[2]	0	[1],[2]
Net realized and unrealized gains (losses) on derivative instruments	$ 100,000	[1],[2]

[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] Financial operations derivatives represent interests in variable interest entities as described in Note 18, “Variable Interest Entities".