Derivative Financial Instruments (Details 2) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014		Jun. 30, 2015	Jun. 30, 2014		Dec. 31, 2014
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income		$ (73,356)	$ 47,515		$ (18,672)	$ 47,487
Net investment income
Derivatives not designated as hedging instruments
Change in fair value of GLWB		(6,258)	609		(3,488)	609
Policyholders' Funds
Derivatives not designated as hedging instruments
Embedded derivatives - GLWB		2,919			2,919			$ 6,407
Futures on equity indices | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	271	13		418	90
Futures on equity indices | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	(266)	(196)		(989)	(359)
Interest rate swaps | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	(8,749)	941		(5,927)	2,050
Interest rate swaps | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	0	0
Interest rate futures | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	36	(62)		(115)	(65)
Interest rate futures | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	37	111		172	87
Interest rate swaptions | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	1,081	640		1,991	842
Interest rate swaptions | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	(1,089)	(877)		(2,076)	(1,710)
Other forward contracts | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	(34,585)	20,402		(17,760)	14,060
Other forward contracts | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	7,250	31,996		(2,090)	39,577
Cross-currency swaps | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	(37,342)	(5,453)		7,704	(7,085)
Cash flow hedges:
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)		(16,633)	3,010		522	3,894
Gain (loss) reclassified from OCI into net income (Effective portion)		2,091	4,005		4,349	4,585
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)		(2,515)	3,900		626	5,144
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)		1,837	3,142	[1]	3,693	3,705	[1]
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)		0	0		0	0
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)		(22)	18	[1]	(43)	0	[1]
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)		(14,118)	(890)		(104)	(1,250)
Cash flow hedges: | Cross-currency 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)		276	845	[1]	699	845	[1]
Cash flow hedges: | Cross-currency swaps | Realized investment gains (losses)
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) reclassified from OCI into net income (Effective portion)					0	35	[2]
Fair value hedges:
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income		381	(1,333)		(427)	(2,400)
Gain (loss) on hedged assets recognized in net income		(385)	1,333		428	2,400
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		569	(1,333)	[1]	(869)	(2,400)	[1]
Gain (loss) on hedged assets recognized in net income		(573)	1,333	[1]	870	2,400	[1]
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		(188)	0	[2]	442	0	[2]
Gain (loss) on hedged assets recognized in net income		$ 188	$ 0	[2]	$ (442)	$ 0	[2]

[1] Net investment income.

[2] Represents realized gains (losses) on closed positions recorded in realized investment gains (losses), net.