Investment Information - Summary of available for sale securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Available for sale securities:
Estimated fair value	$ 21,014,451	$ 19,732,825
Gross Unrealized Gains	89,234	198,691
Gross Unrealized Losses	(1,648,287)	(171,544)
Allowance for Expected Credit Losses	(41,355)	(2,883)
Cost or Amortized Cost	22,614,859	19,708,561
Fixed maturities available for sale, at fair value
Available for sale securities:
Estimated fair value	19,682,789	17,998,109
Gross Unrealized Gains	88,680	198,123
Gross Unrealized Losses	(1,646,399)	(170,954)
Allowance for Expected Credit Losses	(41,355)	(2,883)	$ (2,397)
Cost or Amortized Cost	21,281,863	17,973,823
Fixed maturities available for sale, at fair value \| Corporate bonds
Available for sale securities:
Estimated fair value	8,020,128	6,553,333
Gross Unrealized Gains	55,468	104,170
Gross Unrealized Losses	(781,353)	(69,194)
Allowance for Expected Credit Losses	(29,950)	(2,037)
Cost or Amortized Cost	8,775,963	6,520,394
Fixed maturities available for sale, at fair value \| Mortgage backed securities
Available for sale securities:
Estimated fair value	795,391	408,477
Gross Unrealized Gains	4,933	2,825
Gross Unrealized Losses	(86,587)	(5,410)
Allowance for Expected Credit Losses	2	(48)
Cost or Amortized Cost	877,043	411,110
Fixed maturities available for sale, at fair value \| Municipal bonds
Available for sale securities:
Estimated fair value	419,166	404,666
Gross Unrealized Gains	3,149	18,724
Gross Unrealized Losses	(33,360)	(1,409)
Allowance for Expected Credit Losses	(100)	(2)	(11)
Cost or Amortized Cost	449,477	387,353
Fixed maturities available for sale, at fair value \| Commercial mortgage backed securities
Available for sale securities:
Estimated fair value	1,047,275	1,046,484
Gross Unrealized Gains	608	1,740
Gross Unrealized Losses	(57,667)	(3,117)
Allowance for Expected Credit Losses	(3,415)	(6)
Cost or Amortized Cost	1,107,749	1,047,867
Fixed maturities available for sale, at fair value \| US government and government agencies
Available for sale securities:
Estimated fair value	5,161,193	4,772,764
Gross Unrealized Gains	14,891	10,076
Gross Unrealized Losses	(342,963)	(45,967)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	5,489,265	4,808,655
Fixed maturities available for sale, at fair value \| Non-US government securities
Available for sale securities:
Estimated fair value	2,312,819	2,120,294
Gross Unrealized Gains	8,870	54,048
Gross Unrealized Losses	(237,846)	(34,749)
Allowance for Expected Credit Losses	(1,882)	(82)	$ 0
Cost or Amortized Cost	2,543,677	2,101,077
Fixed maturities available for sale, at fair value \| Asset backed securities
Available for sale securities:
Estimated fair value	1,926,817	2,692,091
Gross Unrealized Gains	761	6,540
Gross Unrealized Losses	(106,623)	(11,108)
Allowance for Expected Credit Losses	(6,010)	(708)
Cost or Amortized Cost	2,038,689	2,697,367
Short-term investments
Available for sale securities:
Estimated fair value	1,331,662	1,734,716
Gross Unrealized Gains	554	568
Gross Unrealized Losses	(1,888)	(590)
Allowance for Expected Credit Losses	0	0
Cost or Amortized Cost	$ 1,332,996	$ 1,734,738

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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