Derivative Instruments - Derivatives Designated As Fair Value Hedges (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	$ 1,475	$ (2,439)
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	30,245	(20,557)
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	1,475	(2,439)
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	(5,457)
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	30,245	(15,100)
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	3,607
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	$ (28,770)	$ 14,511