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, 2022	Dec. 31, 2021
Derivative [Line Items]
Notional Value	$ 510,544	$ 480,991
Derivatives	24,712	15,422
Derivatives	13,712	16,923
Gains (Losses)	41,068	(13,298)
Exchange-traded futures
Derivative [Line Items]
Notional Value	154,687	131,876
Derivatives	1,768	392
Derivatives	162	1,186
Gains (Losses)	19,994	(5,072)
Currency forwards
Derivative [Line Items]
Notional Value	34,597	66,058
Derivatives	4,446	7,344
Derivatives	5,047	6,980
Gains (Losses)	1,965	1,746
Interest rate swaps
Derivative [Line Items]
Notional Value	16,847	13,483
Derivatives	386	497
Derivatives	262	833
Gains (Losses)	70	(316)
Credit default swaps
Derivative [Line Items]
Notional Value	225,671	155,757
Derivatives	17,507	6,594
Derivatives	7,302	6,967
Gains (Losses)	(1,000)	(2,914)
Total return swaps
Derivative [Line Items]
Notional Value	50,000	63,817
Derivatives	0	595
Derivatives	6	527
Gains (Losses)	5,211	(6,433)
Option swaps
Derivative [Line Items]
Notional Value	28,742	50,000
Derivatives	605	0
Derivatives	933	430
Gains (Losses)	$ 14,828	$ (309)