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Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned | $ 261,367 | $ 256,113 | $ 243,562 | $ 260,901 | $ 266,267 | $ 267,857 | $ 247,102 | $ 249,762 | $ 1,021,943 | $ 1,030,988 | $ 975,162
Investment income, net of expenses | 36,118 | 37,252 | 39,679 | 41,347 | 41,322 | 42,715 | 42,423 | 40,585 | 154,396 | 167,045 | 141,331
Realized gains (losses) | 2,901 | 2,259 | 6,701 | 1,891 | 1,320 | 4,205 | 307 | (526) | 13,752 | 5,306 | (1,353)
Other revenue | 1,895 | 380 | 4,026 | 2,754 | 2,717 | 3,606 | 2,485 | 1,830 | 9,055 | 10,638 | 8,708
Loss incurred, net | 45,758 | 40,686 | 217,374 | 60,956 | 23,690 | 33,985 | 21,836 | 39,064 | 364,774 | 118,575 | 36,562
Underwriting and other expenses, net | 66,311 | 64,253 | 60,111 | 57,698 | 65,227 | 61,278 | 59,270 | 61,650 | 248,373 | 247,425 |
Loss on debt extinguishment | 0 | 26,736 | 0 | 0 |  |  |  |  | 26,736 | 0 | 0
Provision for income tax | 38,782 | 33,518 | 2,436 | 38,434 | 45,599 | 46,186 | 43,433 | 38,996 | 113,170 | 174,214 | 174,053
Net income | $ 151,430 | $ 130,811 | $ 14,047 | $ 149,805 | $ 177,110 | $ 176,934 | $ 167,778 | $ 151,941 | $ 446,093 | $ 673,763 | $ 670,097
Earnings per Share [Abstract] |  |  |  |  |  |  |  |  |  |  |
Basic (in dollars per share) | $ 0.45 | $ 0.39 | $ 0.04 | $ 0.44 | $ 0.51 | $ 0.50 | $ 0.47 | $ 0.43 | $ 1.31 | $ 1.91 | $ 1.83
Diluted (in dollars per share) | $ 0.44 | $ 0.38 | $ 0.04 | $ 0.42 | $ 0.49 | $ 0.49 | $ 0.46 | $ 0.42 | $ 1.29 | $ 1.85 | $ 1.78

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