Derivative Instruments - Net Realized and unrealized gains (losses) on Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative [Line Items]
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	$ 1,475	$ (2,439)
Net realized and unrealized gains (losses) on derivative instruments	7,885	702
Derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	6,410	3,141
Derivatives not designated as hedging instruments | Investment related derivatives
Derivative [Line Items]
Interest rate exposure	200	700
Foreign exchange exposure	(1,598)	(354)
Credit exposure	(816)	(3,699)
Financial market exposure	5,353	3,944
Derivatives not designated as hedging instruments | Financial operations derivatives
Derivative [Line Items]
Credit exposure	242	143
Derivatives not designated as hedging instruments | Other non-investment derivatives
Derivative [Line Items]
Guaranteed minimum income benefit contract	3,697	2,015
Gain Loss On Modified Coinsurance Funds Withheld Contract Not Designated As Hedging Instruments	$ (668)	$ 392