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Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Deferred policy acquisition costs |  | $ 326,915 |  | $ 288,578 |  | $ 271,186 |
Reserve for loss and loss expenses |  | 4,580,903 |  | 4,260,355 |  | 4,067,163 |
Unearned premiums |  | 1,803,207 |  | 1,618,271 |  | 1,523,167 |
Net premiums earned |  | 3,017,253 |  | 2,681,814 |  | 2,597,171 |
Net investment income | [1] | 344,188 |  | 222,890 |  | 236,965 |
Loss and loss expense incurred |  | 1,813,984 |  | 1,635,823 |  | 1,551,491 |
Amortization of deferred policy acquisition costs |  | 626,469 |  | 560,271 |  | 535,973 |
Other operating expenses |  | 358,208 | [2] | 349,371 | [3] | 345,714 | [4]
Net premiums written |  | 3,189,713 |  | 2,773,092 |  | 2,679,424 |
Other insurance expenses |  | 375,931 |  | 366,941 |  | 358,069 |
Other income |  | 17,723 |  | 17,570 |  | 12,355 |
Standard Commercial Lines [Member] |  |  |  |  |  |  |
Deferred policy acquisition costs |  | 279,850 |  | 246,494 |  | 226,464 |
Reserve for loss and loss expenses |  | 3,832,151 |  | 3,596,340 |  | 3,436,363 |
Unearned premiums |  | 1,346,809 |  | 1,196,243 |  | 1,108,009 |
Net premiums earned |  | 2,443,885 |  | 2,143,184 |  | 2,049,614 |
Net investment income |  | 0 |  | 0 |  | 0 |
Loss and loss expense incurred |  | 1,426,768 |  | 1,245,627 |  | 1,187,856 |
Amortization of deferred policy acquisition costs |  | 539,606 |  | 474,322 |  | 445,661 |
Other operating expenses |  | 278,915 |  | 271,504 |  | 270,107 |
Net premiums written |  | 2,593,018 |  | 2,230,636 |  | 2,137,071 |
Other income |  | 16,056 |  | 15,512 |  | 10,889 |
E&S Lines [Member] |  |  |  |  |  |  |
Deferred policy acquisition costs |  | 34,154 |  | 28,281 |  | 27,874 |
Reserve for loss and loss expenses |  | 478,686 |  | 435,667 |  | 406,600 |
Unearned premiums |  | 139,122 |  | 113,845 |  | 106,033 |
Net premiums earned |  | 279,809 |  | 239,490 |  | 239,818 |
Net investment income |  | 0 |  | 0 |  | 0 |
Loss and loss expense incurred |  | 175,100 |  | 156,936 |  | 152,335 |
Amortization of deferred policy acquisition costs |  | 60,945 |  | 55,255 |  | 55,835 |
Other operating expenses |  | 27,734 |  | 27,173 |  | 21,905 |
Net premiums written |  | 304,430 |  | 247,290 |  | 237,761 |
Miscellaneous Income [Member] |  |  |  |  |  |  |
Other income |  | 17,723 |  | 17,570 |  | 12,355 |
Standard Personal Lines |  |  |  |  |  |  |
Deferred policy acquisition costs |  | 12,911 |  | 13,803 |  | 16,848 |
Reserve for loss and loss expenses |  | 270,066 |  | 228,348 |  | 224,200 |
Unearned premiums |  | 317,276 |  | 308,183 |  | 309,125 |
Net premiums earned |  | 293,559 |  | 299,140 |  | 307,739 |
Net investment income |  | 0 |  | 0 |  | 0 |
Loss and loss expense incurred |  | 212,116 |  | 233,260 |  | 211,300 |
Amortization of deferred policy acquisition costs |  | 25,918 |  | 30,694 |  | 34,477 |
Other operating expenses |  | 51,559 |  | 50,694 |  | 53,702 |
Net premiums written |  | 292,265 |  | 295,166 |  | 304,592 |
Other income |  | 1,667 |  | 2,058 |  | 1,466 |
Investments SIGI |  |  |  |  |  |  |
Deferred policy acquisition costs |  | 0 |  | 0 |  | 0 |
Reserve for loss and loss expenses |  | 0 |  | 0 |  | 0 |
Unearned premiums |  | 0 |  | 0 |  | 0 |
Net premiums earned |  | 0 |  | 0 |  | 0 |
Net investment income | [1] | 344,188 |  | 222,890 |  | 236,965 |
Loss and loss expense incurred |  | 0 |  | 0 |  | 0 |
Amortization of deferred policy acquisition costs |  | 0 |  | 0 |  | 0 |
Other operating expenses |  | 0 |  | 0 |  | 0 |
Net premiums written |  | $ 0 |  | $ 0 |  | $ 0 |
[1] | Includes “Net investment income earned” and “Net realized and unrealized investment gains (losses)” on the Consolidated Statements of Income.
[2] | “Other operating expenses” of $358,208 reconciles to the Consolidated Statements of Income
[3] | “Other operating expenses” of $349,371 reconciles to the Consolidated Statements of Income
[4] | “Other operating expenses” of $345,714 reconciles to the Consolidated Statements of Income

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