Derivative Instruments - Gains and Losses for Derivative Instruments Recognized in Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Derivative [Line Items]
Net (losses) gains on derivative instruments	$ (10,494)	$ 19,732
Exchange-traded futures
Derivative [Line Items]
Net (losses) gains on derivative instruments	(4,632)	7,513
Currency forwards
Derivative [Line Items]
Net (losses) gains on derivative instruments	(105)	544
Interest rate swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	(63)	(73)
Credit default swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	(2,228)	1,717
Total return swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	(2,056)	7,406
Option swaps
Derivative [Line Items]
Net (losses) gains on derivative instruments	$ (1,410)	$ 2,625