Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	$ (573)	$ (54,880)	$ (19,556)
Interest rate swaps \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	8,620	(12,351)	4,036
Interest rate swaps \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(4,979)	(38,377)	(4,476)
Interest rate futures \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	164	260	(3,600)
Interest rate futures \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(2,641)	(251)	(11,640)
Futures on equity indices \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	2	(32)	(9)
Futures on equity indices \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(774)	373	(363)
Interest rate swaptions \| Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	862	(3,798)	(3,450)
Interest rate swaptions \| Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(1,827)	(704)	(54)
Cash flow hedges
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	(18,881)	21,014	17,293
Gain (loss) reclassified from OCI into net income (Effective portion)	2,919	2,863	1,691
Gain (loss) recognized in net income on derivatives (Ineffective portion and amount excluded from effectiveness testing)		(77)	637
Cash flow hedges \| Interest rate swaps
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	5,220	21,322	13,896
Cash flow hedges \| Interest rate swaps \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)	2,856	2,820	1,582
Gain (loss) recognized in net income on derivatives (Ineffective portion and amount excluded from effectiveness testing)		9
Cash flow hedges \| Cross-currency swaps
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	(24,101)	1,123	3,065
Cash flow hedges \| Interest rate futures
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)		(1,431)	332
Cash flow hedges \| Interest rate futures \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)	63	43	110
Gain (loss) recognized in net income on derivatives (Ineffective portion and amount excluded from effectiveness testing)		(92)	92
Cash flow hedges \| Interest rate futures \| Realized investment gains (losses)
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in net income on derivatives (Ineffective portion and amount excluded from effectiveness testing)		6	545
Fair value hedges
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	(380)	(9,607)	(2,115)
Gain (loss) on hedged assets recognized in net income	380	7,479	3,632
Hedge ineffectiveness	0	(2,128)	1,517
Fair value hedges \| Interest rate swaps \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	(380)	(1,011)
Gain (loss) on hedged assets recognized in net income	380	1,011
Fair value hedges \| Interest rate futures \| Net investment income
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income		(285)	(1,027)
Gain (loss) on hedged assets recognized in net income		(2,002)	3,632
Fair value hedges \| Interest rate futures \| Realized investment gains (losses)
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income		(8,311)	(1,088)
Gain (loss) on hedged assets recognized in net income		$ 8,470

The amount recognized in earnings related to the change in fair value during the period of derivative or nonderivative instruments designated as fair value hedging instruments.

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The amount recognized in earnings related to the change in fair value during the period of the hedged item in a fair value hedge.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Net gain (loss) from the increase (decrease) in fair value of derivative instrument not designated as hedging instrument.

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Net gain (loss) recognized in earnings during the reporting period representing the amount of the fair value of the hedges' ineffectiveness.

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