Derivative Financial Instruments (Details 2) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014		Sep. 30, 2015	Sep. 30, 2014		Dec. 31, 2014
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income		$ 86,668	$ 18,857		$ 67,996	$ 66,344
Net investment income
Derivatives not designated as hedging instruments
Change in fair value of GLWB		6,858	1,494		3,370	2,103
Policyholders' Funds
Derivatives not designated as hedging instruments
Embedded derivatives - GLWB		9,777			9,777			$ 6,407
Futures on equity indices | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	478	222		896	312
Futures on equity indices | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	1,111	(72)		122	(431)
Interest rate swaps | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	6,480	467		553	2,517
Interest rate futures | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	(99)	10		(214)	(55)
Interest rate futures | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	(117)	65		55	152
Interest rate swaptions | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	928	835		2,919	1,677
Interest rate swaptions | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	0	(917)		(2,076)	(2,627)
Other forward contracts | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	32,538	(16,147)		14,778	(2,087)
Other forward contracts | Realized investment gains (losses)
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[2]	8,504	16,894		6,414	56,471
Cross-currency swaps | Net investment income
Derivatives not designated as hedging instruments
Gain (loss) on derivatives recognized in net income	[1]	36,845	17,500		44,549	10,415
Cash flow hedges:
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) recognized in OCI on derivatives (Effective portion)		14,804	7,408		15,326	11,302
Gain (loss) reclassified from OCI into net income (Effective portion)		2,099	2,639		6,448	7,224
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)		(937)	184		(311)	5,328
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)		1,490	1,876	[1]	5,183	5,581	[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)		(21)	17	[1]	(64)	52	[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)		15,741	7,224		15,637	5,974
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)		630	900	[1]	1,329	1,745	[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	(154)	[2]	0	(154)	[2]
Fair value hedges:
Effect of derivative instruments in the condensed consolidated statement of income
Gain (loss) on derivatives recognized in net income		(297)	395		(724)	(2,005)
Gain (loss) on hedged assets recognized in net income		300	(406)		728	1,994
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		(620)	395	[1]	(1,489)	(2,005)	[1]
Gain (loss) on hedged assets recognized in net income		623	(406)	[1]	1,493	1,994	[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		323	0	[2]	765	0	[2]
Gain (loss) on hedged assets recognized in net income		$ (323)	$ 0	[2]	$ (765)	$ 0	[2]

[1] Net investment income.

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