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, 2023	Dec. 31, 2022
Derivative [Line Items]
Notional Value	$ 446,989	$ 510,544
Derivatives	14,518	24,712
Derivatives	18,180	13,712
Gains (Losses)	(16,410)	41,068
Exchange-traded futures
Derivative [Line Items]
Notional Value	116,344	154,687
Derivatives	1	1,768
Derivatives	3,511	162
Gains (Losses)	(2,038)	19,994
Currency forwards
Derivative [Line Items]
Notional Value	34,440	34,597
Derivatives	4,951	4,446
Derivatives	5,597	5,047
Gains (Losses)	(82)	1,965
Interest rate swaps
Derivative [Line Items]
Notional Value	11,345	16,847
Derivatives	294	386
Derivatives	349	262
Gains (Losses)	110	70
Credit default swaps
Derivative [Line Items]
Notional Value	139,607	225,671
Derivatives	9,265	17,507
Derivatives	4,197	7,302
Gains (Losses)	(6,850)	(1,000)
Total return swaps
Derivative [Line Items]
Notional Value	50,232	50,000
Derivatives	1	0
Derivatives	135	6
Gains (Losses)	(2,107)	5,211
Option swaps
Derivative [Line Items]
Notional Value	95,021	28,742
Derivatives	6	605
Derivatives	4,391	933
Gains (Losses)	$ (5,443)	$ 14,828