Derivative Instruments - Gains and Losses for Derivative Instruments Recognized in Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Derivative [Line Items]
Net (losses) gains on derivative instruments	$ (861)	$ 22,099	$ (11,355)	$ 41,831
Exchange-traded futures
Derivative [Line Items]
Net (losses) gains on derivative instruments	2,032	6,441	(2,600)	13,954
Currency forwards
Derivative [Line Items]
Net (losses) gains on derivative instruments	68	1,738	(37)	2,282
Interest rate swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	114	21	51	(52)
Credit default swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	(2,013)	4,720	(4,241)	6,437
Total return swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	(1,645)	8,025	(3,701)	15,431
Option swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	$ 583	$ 1,154	$ (827)	$ 3,779