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Investment Information - Net realized gains and losses (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Available for sale securities: |  |  |  |  |
Available for sale securities, gross gains on investment sales |  | $ 86,819 | $ 104,733 | $ 267,362 | $ 515,086
Available for sale securities, gross losses on investment sales |  | (18,446) | (16,862) | (132,071) | (98,654)
Equity securities, at fair value: |  |  |  |  |
Net realized gains (losses) on sales during the period |  | 14,736 | 26,549 | 86,155 | 7,760
Net unrealized gains (losses) on equity securities still held at reporting date |  | (40,155) | 33,562 | 45,400 | 3,682
Allowance for credit losses: |  |  |  |  |
Allowance for credit losses - underwriting related |  | (3,985) | 351 | 2,664 | (8,753)
Net impairment losses |  |  |  | 0 | (533)
Derivative instruments | [1] | (21,435) | 20,369 | (36,428) | 146,722
Other | [2] | (41,495) | 7,303 | (54,316) | (1,309)
Net realized gains (losses) |  | (25,040) | 280,499 | 320,328 | 470,127
Net loss on deconsolidation |  | 33,100 |  | 33,100 |
Fixed maturities |  |  |  |  |
Available for sale securities: |  |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | (7,492) | 34,115 | 19,973 | (25,370)
Allowance for credit losses: |  |  |  |  |
Allowance for credit losses - investment related |  | (456) | 1,332 | (1,208) | (4,763)
Other investments |  |  |  |  |
Available for sale securities: |  |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | 3,811 | 61,622 | 111,550 | (67,608)
Equity securities |  |  |  |  |
Available for sale securities: |  |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | 3,042 | 4,048 | 10,599 | 5,803
Short-term investments |  |  |  |  |
Available for sale securities: |  |  |  |  |
Change in fair value of assets and liabilities accounted for using the fair value option |  | $ 16 | $ 3,377 | $ 648 | $ (1,936)
[1] | See note 10 for information on the Company’s derivative instruments.
[2] | 2021 periods reflected $33.1 million of losses related to the Company’s deconsolidation of Watford.

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