Fair Value Measurements - Level 3 unobservable inputs (Details 3) - Recurring basis - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Embedded derivatives - GLWB	$ 21,707	$ 11,257
Level 3
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Embedded derivatives - GLWB	$ 21,707	$ 11,257
Level 3 | Internal model pricing | Minimum
Unobservable Input
Equity Volatility	15.00%	15.00%
Swap Curve	0.85%	0.75%
Lapse Rate	1.00%	1.00%
Level 3 | Internal model pricing | Maximum
Unobservable Input
Equity Volatility	28.00%	28.00%
Swap Curve	2.50%	3.00%
Lapse Rate	15.00%	15.00%
Derivative Financial Instruments, Liabilities | Level 3 | Internal model pricing
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Embedded derivatives - GLWB	$ 21,707	$ 11,257