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Investments Realized and Unrealized Gains (Losses) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Gain (Loss) on Securities [Line Items] |  |  |
Gross gains on sales | $ 5,896 | $ 28,419 | $ 15,284
Gross losses on sales | (30,760) | (60,055) | (8,140)
Net realized investment gains (losses) on disposals | (24,864) | (31,636) | 7,144
Net unrealized (losses) gains on equity securities | 9,510 | (32,127) | 17,881
Losses on securities for which we have the intent to sell | (921) | (11,823) | (519)
Net realized and unrealized investment gains (losses) | (3,552) | (114,808) | 17,599
Available-for-sale Securities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Net credit loss (expense) benefit | 12,898 | (39,169) | (6,858)
Held-to-maturity Securities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Net credit loss (expense) benefit | 0 | 63 | (49)
Commercial Mortgage Loans [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Net credit loss (expense) benefit | $ (175) | $ (116) | $ 0

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