Derivative Instruments - Derivatives Designated As Fair Value Hedges (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	$ (506)	$ (2,194)	$ 969	$ (4,633)
Derivatives designated as hedging instruments | Fair value hedges | Net realized and unrealized gains (losses) on derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items - amount of gain (loss) recognized in income attributable to risk	(5,002)	14,567	25,243	(5,990)
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	(506)	(2,194)	969	(4,633)
Derivatives designated as hedging instruments | Fair value hedges | Net realized and unrealized gains (losses) on derivative instruments | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items - amount of gain (loss) recognized in income attributable to risk	0	7,270	0	1,813
Derivatives designated as hedging instruments | Fair value hedges | Net realized and unrealized gains (losses) on derivative instruments | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items - amount of gain (loss) recognized in income attributable to risk	(5,002)	7,297	25,243	(7,803)
Derivatives designated as hedging instruments | Fair value hedges | Net realized and unrealized gains (losses) on derivative instruments | Deposit liabilities
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items - amount of gain (loss) recognized in income attributable to risk	0	(9,789)	0	(6,182)
Derivatives designated as hedging instruments | Fair value hedges | Net realized and unrealized gains (losses) on derivative instruments | Fixed maturity investments
Derivative Instruments, Gain (Loss) [Line Items]
Hedged items - amount of gain (loss) recognized in income attributable to risk	$ 4,496	$ (6,972)	$ (24,274)	$ 7,539