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Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
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Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | $ 15,389,158 | $ 12,238,683
Estimated Fair Value - 12 Months or More | 888,195 | 297,357
Estimated Fair Value | 16,277,353 | 12,536,040
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (650,472) | (157,279)
Gross Unrealized Losses - 12 Months or More | (76,180) | (14,265)
Gross Unrealized Losses | (726,652) | (171,544)
Fixed maturities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 14,969,001 | 11,953,950
Estimated Fair Value - 12 Months or More | 888,195 | 297,357
Estimated Fair Value | 15,857,196 | 12,251,307
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (649,825) | (156,689)
Gross Unrealized Losses - 12 Months or More | (76,180) | (14,265)
Gross Unrealized Losses | (726,005) | (170,954)
Fixed maturities | Corporate bonds |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 5,798,556 | 3,639,582
Estimated Fair Value - 12 Months or More | 513,866 | 98,867
Estimated Fair Value | 6,312,422 | 3,738,449
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (305,661) | (63,938)
Gross Unrealized Losses - 12 Months or More | (50,803) | (5,256)
Gross Unrealized Losses | (356,464) | (69,194)
Fixed maturities | Mortgage backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 328,090 | 222,176
Estimated Fair Value - 12 Months or More | 68,490 | 46,809
Estimated Fair Value | 396,580 | 268,985
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (21,714) | (3,545)
Gross Unrealized Losses - 12 Months or More | (6,716) | (1,865)
Gross Unrealized Losses | (28,430) | (5,410)
Fixed maturities | Municipal bonds |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 203,717 | 26,665
Estimated Fair Value - 12 Months or More | 14,759 | 16,361
Estimated Fair Value | 218,476 | 43,026
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (9,578) | (385)
Gross Unrealized Losses - 12 Months or More | (1,322) | (1,024)
Gross Unrealized Losses | (10,900) | (1,409)
Fixed maturities | Commercial mortgage backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 942,203 | 675,603
Estimated Fair Value - 12 Months or More | 1,654 | 5,908
Estimated Fair Value | 943,857 | 681,511
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (15,815) | (2,805)
Gross Unrealized Losses - 12 Months or More | (47) | (312)
Gross Unrealized Losses | (15,862) | (3,117)
Fixed maturities | US government and government agencies |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 4,201,416 | 4,211,621
Estimated Fair Value - 12 Months or More | 80,735 | 33,373
Estimated Fair Value | 4,282,151 | 4,244,994
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (173,754) | (44,180)
Gross Unrealized Losses - 12 Months or More | (5,082) | (1,787)
Gross Unrealized Losses | (178,836) | (45,967)
Fixed maturities | Non-US government securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 2,045,013 | 1,511,301
Estimated Fair Value - 12 Months or More | 98,575 | 62,957
Estimated Fair Value | 2,143,588 | 1,574,258
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (82,107) | (31,983)
Gross Unrealized Losses - 12 Months or More | (9,933) | (2,766)
Gross Unrealized Losses | (92,040) | (34,749)
Fixed maturities | Asset backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 1,450,006 | 1,667,002
Estimated Fair Value - 12 Months or More | 110,116 | 33,082
Estimated Fair Value | 1,560,122 | 1,700,084
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (41,196) | (9,853)
Gross Unrealized Losses - 12 Months or More | (2,277) | (1,255)
Gross Unrealized Losses | (43,473) | (11,108)
Short-term investments |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract] |  |
Estimated Fair Value - Less than 12 Months | 420,157 | 284,733
Estimated Fair Value - 12 Months or More | 0 | 0
Estimated Fair Value | 420,157 | 284,733
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract] |  |
Gross Unrealized Losses - Less than 12 Months | (647) | (590)
Gross Unrealized Losses - 12 Months or More | 0 | 0
Gross Unrealized Losses | $ (647) | $ (590)

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456 + Details
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