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Debt Securities - Debt securities in an unrealized loss position (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Fair Value |  |
Less than 12 months | $ 49,649 | $ 1,070,674
12 months or more | 2,122,190 | 1,368,859
Total | 2,171,839 | 2,439,533
Unrealized Losses |  |
Less than 12 months | (1,237) | (81,841)
Unrealized Losses | (333,315) | (229,363)
Total | (334,552) | (311,204)
Fair Value |  |
Less than 12 months |  | 58,065
12 months or more | 701,676 | 727,230
Total | 701,676 | 785,295
Unrealized Losses |  |
Less than 12 months |  | (8,009)
12 months or more | (180,938) | (125,008)
Total | (180,938) | (133,017)
U.S. Treasury securities |  |
Fair Value |  |
Less than 12 months | 0 | 74
12 months or more | 50,130 | 113,987
Total | 50,130 | 114,061
Unrealized Losses |  |
Less than 12 months | 0 | 0
Unrealized Losses | (1,392) | (3,744)
Total | (1,392) | (3,744)
Obligations of U.S. government corporations and agencies |  |
Fair Value |  |
Less than 12 months | 1,983 | 19,603
12 months or more | 7,699 | 0
Total | 9,682 | 19,603
Unrealized Losses |  |
Less than 12 months | (6) | (321)
Unrealized Losses | (248) | 0
Total | (254) | (321)
Obligations of states and political subdivisions |  |
Fair Value |  |
Less than 12 months | 45,778 | 166,147
12 months or more | 177,195 | 75,217
Total | 222,973 | 241,364
Unrealized Losses |  |
Less than 12 months | (1,219) | (10,059)
Unrealized Losses | (26,539) | (16,016)
Total | (27,758) | (26,075)
Asset-backed securities |  |
Fair Value |  |
Less than 12 months | 0 | 390,164
12 months or more | 479,448 | 79,711
Total | 479,448 | 469,875
Unrealized Losses |  |
Less than 12 months | 0 | (15,648)
Unrealized Losses | (7,069) | (4,035)
Total | (7,069) | (19,683)
Commercial mortgage-backed securities |  |
Fair Value |  |
Less than 12 months | 0 | 89,428
12 months or more | 100,300 | 18,966
Total | 100,300 | 108,394
Unrealized Losses |  |
Less than 12 months | 0 | (12,623)
Unrealized Losses | (19,817) | (3,406)
Total | (19,817) | (16,029)
Fair Value |  |
Less than 12 months |  | 58,065
12 months or more | 366,465 | 353,017
Total | 366,465 | 411,082
Unrealized Losses |  |
Less than 12 months |  | (8,009)
12 months or more | (93,401) | (55,729)
Total | (93,401) | (63,738)
Residential mortgage-backed securities |  |
Fair Value |  |
Less than 12 months | 431 | 366,221
12 months or more | 1,088,344 | 876,668
Total | 1,088,775 | 1,242,889
Unrealized Losses |  |
Less than 12 months | (10) | (38,111)
Unrealized Losses | (254,518) | (182,606)
Total | (254,528) | (220,717)
Fair Value |  |
Less than 12 months |  | 0
12 months or more | 335,211 | 374,213
Total | 335,211 | 374,213
Unrealized Losses |  |
Less than 12 months |  | 0
12 months or more | (87,537) | (69,279)
Total | (87,537) | (69,279)
Corporate debt securities |  |
Fair Value |  |
Less than 12 months | 1,457 | 39,037
12 months or more | 219,074 | 204,310
Total | 220,531 | 243,347
Unrealized Losses |  |
Less than 12 months | (2) | (5,079)
Unrealized Losses | (23,732) | (19,556)
Total | $ (23,734) | $ (24,635)

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