Fair Value Measurements - Level 3 unobservable inputs (Details 3) (Recurring basis, Level 3, USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Significant unobservable inputs used during the valuation of assets categorized within Level 3 of the recurring fair value measurements table
Embedded derivatives - GLWB	9,177	6,407
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	9,177	6,407
Internal model pricing | Minimum
Unobservable Input
Equity Volatility	15.00%	15.00%
Swap Curve	0.80%	0.44%
Lapse Rate	1.00%	1.00%
Internal model pricing | Maximum
Unobservable Input
Equity Volatility	28.00%	28.00%
Swap Curve	2.50%	2.70%
Lapse Rate	12.00%	12.00%