Investment Information - Other investments (Details) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		$ 4,071,497	$ 3,824,796
Other investable assets	[1]	500,000	500,000
Other investments (portion measured at fair value: $4,071,497 and $3,824,796)		4,571,497	4,324,796
Fair value option | Fixed maturities
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		995,980	843,354
Fair value option | Other investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		2,370,472	2,331,885
Fair value option | Other investments | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		1,333,014	1,231,731
Fair value option | Other investments | Lending
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		638,786	572,636
Fair value option | Other investments | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		73,171	90,780
Fair value option | Other investments | Energy
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		84,891	65,813
Fair value option | Other investments | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		110,375	138,646
Fair value option | Other investments | Infrastructure
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		32,109	165,516
Fair value option | Other investments | Private equity
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		70,878	48,750
Fair value option | Other investments | Real estate
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		27,248	18,013
Fair value option | Short-term investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		610,114	557,008
Fair value option | Equity securities
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		$ 94,931	$ 92,549

[1] Participation interests in a receivable of a reverse repurchase agreement