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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Derivative [Line Items]
Net gains (losses) on derivative instruments	$ 22,099	$ (11,414)	$ 41,831	$ (9,078)
Exchange-traded futures
Derivative [Line Items]
Net gains (losses) on derivative instruments	6,441	(4,882)	13,954	(3,747)
Currency forwards
Derivative [Line Items]
Net gains (losses) on derivative instruments	1,738	(354)	2,282	827
Interest rate swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	21	(111)	(52)	(23)
Credit default swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	4,720	(1,714)	6,437	(2,236)
Total return swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	8,025	(2,980)	15,431	(3,887)
Option swaps
Derivative [Line Items]
Net gains (losses) on derivative instruments	$ 1,154	$ (1,373)	$ 3,779	$ (12)