Derivative Instruments - Notional Value, Fair Value and Gains and Losses Recognized in Investment Gains (Losses) (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Value	$ 480,991	$ 489,985
Derivatives	15,422	21,741
Derivatives	16,923	30,537
Gains (Losses)	(13,298)	(35,589)
Exchange-traded futures
Derivative [Line Items]
Notional Value	131,876	142,886
Derivatives	392	118
Derivatives	1,186	1,834
Gains (Losses)	(5,072)	(15,743)
Currency forwards
Derivative [Line Items]
Notional Value	66,058	63,906
Derivatives	7,344	8,576
Derivatives	6,980	8,451
Gains (Losses)	1,746	(1,779)
Interest rate swaps
Derivative [Line Items]
Notional Value	13,483	60,997
Derivatives	497	2,043
Derivatives	833	2,955
Gains (Losses)	(316)	(347)
Credit default swaps
Derivative [Line Items]
Notional Value	155,757	167,649
Derivatives	6,594	10,910
Derivatives	6,967	13,304
Gains (Losses)	(2,914)	(104)
Total return swaps
Derivative [Line Items]
Notional Value	63,817	52,061
Derivatives	595	94
Derivatives	527	1,847
Gains (Losses)	(6,433)	(15,242)
Option swaps
Derivative [Line Items]
Notional Value	50,000	2,486
Derivatives	0	0
Derivatives	430	2,146
Gains (Losses)	$ (309)	$ (2,374)