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Property and Casualty Unpaid Claims and Claim Expenses - Incurred and Paid Claims by Accident Year on a Net Basis (Details) $ in Thousands | Dec. 31, 2019 USD ($) claim | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2012 USD ($) | Dec. 31, 2011 USD ($) | Dec. 31, 2010 USD ($)
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Homeowners |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | $ 1,248,333 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | 1,212,885 |  |  |  |  |  |  |  |  |
Outstanding prior to 2010 | 32 |  |  |  |  |  |  |  |  |
Prior years paid | 668 |  |  |  |  |  |  |  |  |
Liabilities for claims and claim adjustment expenses, net of reinsurance | 35,480 |  |  |  |  |  |  |  |  |
Homeowners | 2010 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 132,627 | $ 132,627 | $ 132,905 | $ 132,859 | $ 133,136 | $ 133,216 | $ 133,235 | $ 133,358 | $ 136,907 | $ 140,994
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 25,150,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 132,602 | 132,602 | 132,602 | 132,599 | 132,604 | 132,523 | 132,246 | 129,790 | 124,326 | 98,190
Homeowners | 2011 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 148,067 | 148,079 | 148,370 | 148,414 | 148,755 | 148,860 | 150,791 | 150,334 | 150,141 |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 29,531,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 148,067 | 148,069 | 148,014 | 148,026 | 147,451 | 146,908 | 145,852 | 142,846 | 123,046 |
Homeowners | 2012 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 106,028 | 106,000 | 106,348 | 106,308 | 106,486 | 109,360 | 109,156 | 108,754 |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 21,578,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 106,021 | 105,993 | 105,909 | 105,561 | 105,156 | 104,203 | 101,566 | 84,260 |  |
Homeowners | 2013 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 101,709 | 101,769 | 102,345 | 102,407 | 103,982 | 107,489 | 105,584 |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 19,221,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 101,709 | 101,677 | 101,527 | 100,968 | 99,361 | 96,599 | 76,890 |  |  |
Homeowners | 2014 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 106,458 | 106,554 | 106,844 | 109,059 | 113,505 | 111,647 |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 59 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 20,084,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 106,388 | 106,258 | 106,081 | 105,704 | 103,030 | 83,314 |  |  |  |
Homeowners | 2015 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 115,050 | 114,053 | 114,404 | 115,134 | 111,706 |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 276 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 18,714,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 114,648 | 113,321 | 111,882 | 109,303 | 90,704 |  |  |  |  |
Homeowners | 2016 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 117,933 | 117,009 | 118,604 | 115,931 |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 280 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 19,853,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 117,537 | 115,053 | 113,186 | 95,772 |  |  |  |  |  |
Homeowners | 2017 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 132,666 | 129,818 | 126,285 |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 2,285 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 19,827,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 129,767 | 128,518 | 106,800 |  |  |  |  |  |  |
Homeowners | 2018 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 157,404 | 166,793 |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 4,170 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 20,954,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 152,356 | 130,548 |  |  |  |  |  |  |  |
Homeowners | 2019 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 130,391 |  |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 16,842 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 16,155,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 103,790 |  |  |  |  |  |  |  |  |
Auto liability |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 1,671,607 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | 1,468,500 |  |  |  |  |  |  |  |  |
Outstanding prior to 2010 | 73 |  |  |  |  |  |  |  |  |
Prior years paid | (219) |  |  |  |  |  |  |  |  |
Liabilities for claims and claim adjustment expenses, net of reinsurance | 203,180 |  |  |  |  |  |  |  |  |
Auto liability | 2010 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 149,481 | 149,542 | 149,425 | 149,818 | 151,653 | 152,483 | 154,222 | 156,369 | 160,058 | 157,712
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 48,942,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 149,474 | 149,439 | 149,364 | 149,247 | 148,751 | 147,337 | 144,255 | 137,012 | 118,345 | 63,416
Auto liability | 2011 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 138,849 | 138,949 | 138,891 | 139,840 | 142,488 | 143,133 | 145,735 | 146,713 | 150,803 |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 94 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 45,976,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 138,692 | 138,689 | 138,358 | 138,151 | 136,906 | 133,931 | 126,812 | 108,837 | 61,070 |
Auto liability | 2012 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 145,515 | 145,620 | 145,847 | 147,594 | 149,346 | 150,336 | 153,815 | 156,448 |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 204 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 45,984,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 145,184 | 145,121 | 144,622 | 142,916 | 138,641 | 127,185 | 109,574 | 61,279 |  |
Auto liability | 2013 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 148,135 | 147,993 | 148,111 | 150,657 | 150,720 | 152,858 | 153,860 |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 575 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 47,369,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 147,409 | 146,770 | 145,291 | 139,954 | 131,214 | 108,856 | 62,224 |  |  |
Auto liability | 2014 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 159,355 | 159,794 | 159,937 | 158,470 | 157,249 | 155,105 |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 665 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 49,386,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 157,596 | 155,758 | 149,059 | 139,463 | 117,468 | 61,329 |  |  |  |
Auto liability | 2015 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 178,654 | 178,325 | 177,021 | 172,553 | 165,517 |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 1,850 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 50,618,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 174,495 | 170,088 | 157,980 | 134,473 | 70,836 |  |  |  |  |
Auto liability | 2016 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 186,568 | 184,567 | 184,440 | 180,380 |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 2,649 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 51,995,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 177,834 | 166,815 | 140,901 | 73,073 |  |  |  |  |  |
Auto liability | 2017 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 188,625 | 188,756 | 187,983 |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 8,025 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 48,906,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 166,614 | 139,531 | 70,682 |  |  |  |  |  |  |
Auto liability | 2018 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 195,284 | 200,314 |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 26,931 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 47,078,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 141,537 | 77,528 |  |  |  |  |  |  |  |
Auto liability | 2019 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 181,141 |  |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 64,778 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 42,587,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 69,665 |  |  |  |  |  |  |  |  |
Auto physical damage |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 973,319 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | 968,372 |  |  |  |  |  |  |  |  |
Outstanding prior to 2010 | 0 |  |  |  |  |  |  |  |  |
Prior years paid | 0 |  |  |  |  |  |  |  |  |
Liabilities for claims and claim adjustment expenses, net of reinsurance | 4,947 |  |  |  |  |  |  |  |  |
Auto physical damage | 2010 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 83,011 | 83,018 | 83,028 | 83,036 | 83,050 | 83,052 | 83,046 | 83,103 | 83,420 | 84,112
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 81,581,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 83,009 | 83,015 | 83,028 | 83,036 | 83,051 | 83,067 | 83,087 | 83,103 | 83,120 | $ 79,329
Auto physical damage | 2011 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 85,090 | 85,102 | 85,108 | 85,116 | 85,143 | 85,120 | 86,023 | 85,507 | 86,205 |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 80,804,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 85,090 | 85,095 | 85,108 | 85,116 | 85,127 | 85,148 | 85,181 | 85,254 | $ 83,227 |
Auto physical damage | 2012 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 83,322 | 83,334 | 83,342 | 83,354 | 83,431 | 83,402 | 82,337 | 83,770 |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 78,165,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 83,322 | 83,326 | 83,342 | 83,347 | 83,355 | 83,372 | 83,418 | $ 80,519 |  |
Auto physical damage | 2013 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 88,457 | 88,525 | 88,455 | 88,627 | 88,672 | 88,856 | 91,448 |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 80,920,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 88,452 | 88,471 | 88,484 | 88,532 | 88,580 | 88,688 | $ 85,110 |  |  |
Auto physical damage | 2014 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 95,241 | 95,232 | 95,239 | 95,422 | 95,634 | 95,572 |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ 0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 87,901,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 95,243 | 95,258 | 95,256 | 95,266 | 95,444 | $ 88,939 |  |  |  |
Auto physical damage | 2015 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 97,612 | 97,455 | 97,624 | 97,994 | 99,291 |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ (18) |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 87,497,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 97,625 | 97,638 | 97,685 | 97,850 | $ 92,138 |  |  |  |  |
Auto physical damage | 2016 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 109,603 | 109,348 | 109,515 | 112,430 |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ (17) |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 93,225,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 109,611 | 109,536 | 109,686 | $ 106,459 |  |  |  |  |  |
Auto physical damage | 2017 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 110,520 | 111,798 | 115,483 |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ (161) |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 91,270,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 110,674 | 110,817 | $ 105,156 |  |  |  |  |  |  |
Auto physical damage | 2018 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 108,886 | 109,040 |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ (326) |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 94,388,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 109,103 | $ 103,559 |  |  |  |  |  |  |  |
Auto physical damage | 2019 |  |  |  |  |  |  |  |  |  |
Incurred claims and allocated claim adjustment expense, net of reinsurance | 111,577 |  |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities plus expected development on reported claims | $ (6,829) |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | claim | 89,207,000 |  |  |  |  |  |  |  |  |
Cumulative paid claims and allocated claim adjustment expense, net of reinsurance | $ 106,243 |  |  |  |  |  |  |  |  |

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