Derivative Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	$ 19,429	$ 26,423	$ (47,097)	$ 49,773
Futures on equity indices | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(25)	(4)	61	75
Futures on equity indices | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(330)	(1,077)	(1,442)	(1,299)
Interest rate swaps | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(597)	(267)	(1,912)	8,611
Interest rate swaps | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	14		(622)	(4,432)
Interest rate futures | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(143)	(547)	(663)	(831)
Interest rate futures | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	39	(306)	529	(1,843)
Interest rate swaptions | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	709	124	2,293	358
Interest rate swaptions | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(735)	(495)	(2,043)	(1,265)
Other forward contracts | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	86,590	14,071	55,530	16,833
Other forward contracts | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	(66,093)	14,924	(98,828)	33,566
Cash flow hedges
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)	(49,908)	(8,578)	(33,000)	(1,539)
Gain (loss) reclassified from OCI into net income (Effective portion)	591	723	4,539	2,197
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)	(991)	889	(10,792)	7,095
Gain (loss) reclassified from OCI into net income (Effective portion)	575	707	4,491	2,149
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)	(48,917)	(9,467)	(22,208)	(8,634)
Cash flow hedges | Interest rate futures
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)	16	16	48	48
Fair value hedges
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	338	(69)	7,233	(762)
Gain (loss) on hedged assets recognized in net income	(338)	69	(7,233)	762
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	(1,756)	(69)	5,324	(762)
Gain (loss) on hedged assets recognized in net income	1,768	69	(4,290)	762
Fair value hedges | Interest rate swaps | Realized investment gains (losses)
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income	2,094		1,909
Gain (loss) on hedged assets recognized in net income	$ (2,106)		$ (2,943)