Derivative Instruments - Gains and Losses for Derivative Instruments Recognized in Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Derivative [Line Items]
Net gains (losses) on derivative instruments	$ 14,539	$ 1,895	$ 56,370	$ (7,183)
Exchange-traded futures
Derivative [Line Items]
Net gains (losses) on derivative instruments	9,388	2,186	23,342	(1,561)
Currency forwards
Derivative [Line Items]
Net gains (losses) on derivative instruments	1,318	512	3,600	1,339
Interest rate swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	45	(179)	(7)	(202)
Credit default swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	(1,079)	(91)	5,358	(2,327)
Total return swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	2,970	(611)	18,401	(4,498)
Option swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	$ 1,897	$ 78	$ 5,676	$ 66