Investment Information - Other investments (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		$ 3,935,354	$ 3,824,796
Other investable assets	[1]	500,000	500,000
Other investments (portion measured at fair value: $3,935,354 and $3,824,796)		4,435,354	4,324,796
Fair value option | Fixed maturities
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		900,304	843,354
Fair value option | Other investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		2,318,185	2,331,885
Fair value option | Other investments | Term loan investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		1,187,752	1,231,731
Fair value option | Other investments | Lending
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		606,207	572,636
Fair value option | Other investments | Credit related funds
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		79,355	90,780
Fair value option | Other investments | Energy
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		78,500	65,813
Fair value option | Other investments | Investment grade fixed income
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		142,630	138,646
Fair value option | Other investments | Infrastructure
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		152,352	165,516
Fair value option | Other investments | Private equity
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		52,064	48,750
Fair value option | Other investments | Real estate
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		19,325	18,013
Fair value option | Short-term investments
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		623,930	557,008
Fair value option | Equity securities
Schedule Of Other Investments [Line Items]
Other investments measured at fair value		$ 92,935	$ 92,549

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