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LIABILITY FOR LOSSES AND SETTLEMENT EXPENSES SHORT-DURATION INSURANCE CONTRACTS DEVELOPMENT TABLES (Details)
$ in Thousands
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 ($)
Dec. 31, 2010
USD ($)
Dec. 31, 2009
USD ($)
Dec. 31, 2008
USD ($)
Claims development [Line Items]                    
Liability for losses and settlement expenses, net of reinsurance $ 674,501                  
Commercial Auto Liability [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 425,834                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 314,666                  
All outstanding liabilities before 2008, net of reinsurance (34)                  
Liability for losses and settlement expenses, net of reinsurance 111,134                  
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 26,764 $ 26,768 $ 26,741 $ 26,878 $ 26,923 $ 26,886 $ 27,968 $ 29,433 $ 30,082 $ 29,898
IBNR reserves carried $ (1)                  
Cumulative number of reported claims 11,511                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 26,756 26,750 26,648 26,527 26,306 25,215 23,144 19,204 13,437 6,551
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 24,697 24,655 24,730 24,874 24,986 25,370 26,667 27,923 28,973  
IBNR reserves carried $ 15                  
Cumulative number of reported claims 10,482                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 24,628 24,608 24,593 24,495 24,001 21,532 17,359 12,957 6,952  
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 26,166 26,166 26,479 26,252 26,401 26,478 27,480 30,377    
IBNR reserves carried $ 0                  
Cumulative number of reported claims 11,393                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 26,088 26,039 25,558 24,674 23,547 19,274 13,278 7,025    
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 31,638 31,635 31,914 31,961 31,098 29,790 32,775      
IBNR reserves carried $ 275                  
Cumulative number of reported claims 11,767                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 30,878 30,293 29,121 26,598 22,206 14,875 6,801      
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 37,753 37,693 37,681 37,098 34,235 32,768        
IBNR reserves carried $ (203)                  
Cumulative number of reported claims 11,941                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 36,541 35,406 32,636 26,023 19,398 8,830        
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 43,159 42,336 42,086 40,382 37,265          
IBNR reserves carried $ (52)                  
Cumulative number of reported claims 13,640                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 40,807 36,232 29,997 19,975 8,729          
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 51,933 51,455 49,998 50,342            
IBNR reserves carried $ 1,225                  
Cumulative number of reported claims 15,059                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 44,783 37,433 25,746 12,069            
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 58,627 57,824 53,883              
IBNR reserves carried $ 1,664                  
Cumulative number of reported claims 16,494                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,478 27,424 13,336              
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 61,188 59,468                
IBNR reserves carried $ 6,307                  
Cumulative number of reported claims 16,829                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 30,233 13,583                
Commercial Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 63,909                  
IBNR reserves carried $ 16,652                  
Cumulative number of reported claims 15,220                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 14,474                  
Commercial Property [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 506,617                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 476,074                  
All outstanding liabilities before 2008, net of reinsurance (1)                  
Liability for losses and settlement expenses, net of reinsurance 30,542                  
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 42,786 42,707 42,765 42,784 42,649 42,562 42,422 42,645 42,870 48,559
IBNR reserves carried $ 23                  
Cumulative number of reported claims 15,799                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 42,761 42,755 42,755 42,691 42,607 42,071 41,991 41,868 40,603 31,514
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 36,292 36,020 36,056 35,926 35,622 35,881 35,985 36,003 39,511  
IBNR reserves carried $ (71)                  
Cumulative number of reported claims 14,654                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 36,224 35,893 35,849 35,803 35,803 35,422 34,624 32,602 25,321  
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 39,347 39,428 39,379 39,154 39,071 38,770 38,650 40,422    
IBNR reserves carried $ (75)                  
Cumulative number of reported claims 16,276                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,323 39,318 39,314 38,901 37,926 36,931 35,730 28,032    
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 58,148 58,375 57,703 57,629 57,271 57,614 58,930      
IBNR reserves carried $ 22                  
Cumulative number of reported claims 19,509                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 58,106 57,607 57,065 56,249 54,803 53,226 41,524      
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 46,750 46,566 46,273 45,313 44,157 41,535        
IBNR reserves carried $ 22                  
Cumulative number of reported claims 16,054                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 46,562 46,270 44,543 43,628 41,862 32,879        
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 52,966 53,070 52,511 50,976 50,266          
IBNR reserves carried $ 268                  
Cumulative number of reported claims 16,005                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 52,182 51,457 50,460 47,683 36,555          
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 60,867 60,662 60,990 60,018            
IBNR reserves carried $ 456                  
Cumulative number of reported claims 16,735                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 59,255 58,045 55,679 43,022            
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 55,659 56,798 55,508              
IBNR reserves carried $ 99                  
Cumulative number of reported claims 14,366                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 52,444 50,068 37,208              
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 58,343 59,708                
IBNR reserves carried $ (176)                  
Cumulative number of reported claims 14,866                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 51,103 41,652                
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 55,459                  
IBNR reserves carried $ 65                  
Cumulative number of reported claims 13,818                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 38,114                  
Workers' Compensation [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 467,153                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 363,251                  
All outstanding liabilities before 2008, net of reinsurance 34,420                  
Liability for losses and settlement expenses, net of reinsurance 138,322                  
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 43,272 42,943 43,737 43,301 43,338 43,766 43,156 44,113 46,240 49,577
IBNR reserves carried $ 1,540                  
Cumulative number of reported claims 21,622                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,496 39,099 38,654 37,938 37,270 36,024 34,302 31,110 25,214 12,432
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 43,417 42,774 43,724 43,590 44,093 44,041 44,098 43,335 46,130  
IBNR reserves carried $ 1,642                  
Cumulative number of reported claims 19,236                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,908 39,583 39,167 38,329 37,409 35,363 31,802 25,157 11,879  
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 49,435 49,145 50,069 49,851 49,906 50,057 49,336 46,328    
IBNR reserves carried $ 2,032                  
Cumulative number of reported claims 19,624                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 44,175 43,614 42,651 41,437 39,001 35,029 28,074 14,237    
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 44,056 43,695 44,427 44,506 44,709 46,724 47,836      
IBNR reserves carried $ 1,831                  
Cumulative number of reported claims 19,569                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,167 38,437 37,027 35,295 32,237 26,291 13,291      
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 45,276 45,088 46,928 47,756 50,094 51,099        
IBNR reserves carried $ 2,335                  
Cumulative number of reported claims 19,380                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 40,292 39,456 37,307 33,943 28,109 14,015        
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 45,949 46,102 48,946 51,637 52,141          
IBNR reserves carried $ 2,509                  
Cumulative number of reported claims 19,843                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,254 37,907 35,061 29,219 14,917          
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 47,836 47,472 50,973 51,515            
IBNR reserves carried $ 2,902                  
Cumulative number of reported claims 19,457                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,046 35,883 28,894 14,692            
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 47,227 48,919 54,960              
IBNR reserves carried $ 1,777                  
Cumulative number of reported claims 19,177                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 35,458 29,023 14,956              
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 48,276 57,832                
IBNR reserves carried $ 3,084                  
Cumulative number of reported claims 20,147                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 29,592 15,473                
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 52,409                  
IBNR reserves carried $ 6,721                  
Cumulative number of reported claims 19,181                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,863                  
Other Liability [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 419,036                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 268,726                  
All outstanding liabilities before 2008, net of reinsurance 13,369                  
Liability for losses and settlement expenses, net of reinsurance 163,679                  
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 34,941 35,491 35,528 36,305 37,005 38,755 34,689 38,877 40,005 46,327
IBNR reserves carried $ 538                  
Cumulative number of reported claims 10,957                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 33,451 33,162 32,863 32,514 31,270 28,476 24,139 16,525 10,443 4,299
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 32,063 32,521 32,384 32,827 35,614 34,263 37,650 39,908 44,497  
IBNR reserves carried $ 647                  
Cumulative number of reported claims 9,844                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 30,488 30,176 29,722 28,172 26,255 22,276 16,718 10,707 3,294  
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 33,736 34,556 34,655 36,137 38,829 34,655 36,213 41,624    
IBNR reserves carried $ 639                  
Cumulative number of reported claims 10,144                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 31,776 30,711 29,688 27,612 21,732 15,041 8,315 3,403    
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 31,711 32,452 33,649 35,177 35,125 42,982 44,490      
IBNR reserves carried $ 992                  
Cumulative number of reported claims 9,994                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 29,060 28,228 25,647 22,154 17,308 10,572 4,730      
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 37,180 37,093 40,275 41,139 42,081 42,661        
IBNR reserves carried $ 38                  
Cumulative number of reported claims 10,043                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 32,753 29,651 25,095 19,661 12,851 4,720        
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 39,175 42,187 42,544 43,837 47,974          
IBNR reserves carried $ 3,666                  
Cumulative number of reported claims 10,580                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 31,752 27,642 21,122 11,894 4,414          
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 51,047 52,601 54,403 61,382            
IBNR reserves carried $ 1,662                  
Cumulative number of reported claims 10,878                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 35,318 27,506 17,267 5,630            
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 43,379 47,553 54,221              
IBNR reserves carried $ 9,566                  
Cumulative number of reported claims 10,496                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 19,022 11,588 4,331              
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 56,384 59,052                
IBNR reserves carried $ 12,913                  
Cumulative number of reported claims 10,262                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 18,784 6,403                
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 59,420                  
IBNR reserves carried $ 25,293                  
Cumulative number of reported claims 8,407                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 6,322                  
Personal Auto Liability [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 88,098                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 81,458                  
All outstanding liabilities before 2008, net of reinsurance 71                  
Liability for losses and settlement expenses, net of reinsurance 6,711                  
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 7,804 7,862 7,833 7,876 7,909 8,094 8,098 8,121 8,221 9,024
IBNR reserves carried $ 0                  
Cumulative number of reported claims 6,783                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 7,804 7,805 7,809 7,810 7,794 7,558 7,291 6,743 5,798 3,096
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,312 9,325 9,339 9,382 9,353 9,386 9,452 9,653 10,168  
IBNR reserves carried $ (2)                  
Cumulative number of reported claims 7,523                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,314 9,278 9,204 9,194 9,049 8,905 7,966 6,393 3,564  
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,649 9,676 9,656 9,700 9,698 9,736 9,851 9,815    
IBNR reserves carried $ 2                  
Cumulative number of reported claims 7,431                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,631 9,632 9,562 9,401 9,108 8,250 6,666 3,988    
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,413 9,311 9,460 9,432 9,331 9,388 9,741      
IBNR reserves carried $ 10                  
Cumulative number of reported claims 8,051                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,335 9,153 9,038 8,883 8,129 6,842 3,950      
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 10,626 10,537 10,731 11,023 10,756 10,917        
IBNR reserves carried $ 7                  
Cumulative number of reported claims 7,872                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 10,415 10,244 9,871 9,091 7,439 4,779        
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 10,085 10,085 10,376 10,384 10,492          
IBNR reserves carried $ 22                  
Cumulative number of reported claims 7,235                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,932 9,648 8,985 7,521 4,377          
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,204 9,331 9,631 10,573            
IBNR reserves carried $ 27                  
Cumulative number of reported claims 6,312                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 8,598 7,755 6,392 3,970            
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 8,378 8,638 9,119              
IBNR reserves carried $ 181                  
Cumulative number of reported claims 5,666                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 7,535 6,229 3,800              
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 6,584 7,404                
IBNR reserves carried $ 108                  
Cumulative number of reported claims 4,693                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 5,427 3,505                
Personal Auto Liability [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 7,043                  
IBNR reserves carried $ 553                  
Cumulative number of reported claims 4,427                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 3,467                  
Homeowners Insurance [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 154,254                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 152,114                  
All outstanding liabilities before 2008, net of reinsurance 91                  
Liability for losses and settlement expenses, net of reinsurance 2,231                  
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 19,911 19,908 19,901 19,886 19,886 19,905 19,924 19,894 20,222 22,736
IBNR reserves carried $ 0                  
Cumulative number of reported claims 12,999                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 19,911 19,908 19,902 19,903 19,902 19,891 19,787 19,550 19,385 15,642
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 16,467 16,464 16,465 16,394 16,352 16,379 16,467 16,606 18,109  
IBNR reserves carried $ 0                  
Cumulative number of reported claims 11,486                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,467 16,464 16,421 16,315 16,288 16,246 16,135 15,885 12,645  
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 17,139 17,146 17,129 17,093 17,053 17,074 17,523 17,875    
IBNR reserves carried $ 7                  
Cumulative number of reported claims 12,146                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 17,132 17,130 17,128 17,128 17,011 16,909 16,633 13,457    
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 23,350 23,415 23,448 23,309 22,975 23,389 24,530      
IBNR reserves carried $ (19)                  
Cumulative number of reported claims 14,287                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 23,368 23,370 23,403 23,136 22,737 22,421 19,828      
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 16,879 16,892 16,929 16,836 16,496 16,057        
IBNR reserves carried $ (24)                  
Cumulative number of reported claims 10,113                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,905 16,859 16,793 16,582 16,283 13,759        
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 14,737 14,784 14,685 14,833 14,844          
IBNR reserves carried $ (14)                  
Cumulative number of reported claims 8,688                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 14,703 14,681 14,621 14,285 11,735          
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 13,427 13,447 13,328 13,228            
IBNR reserves carried $ 18                  
Cumulative number of reported claims 7,423                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 13,269 13,215 13,025 11,065            
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 11,041 11,153 11,233              
IBNR reserves carried $ (25)                  
Cumulative number of reported claims 5,940                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 10,730 10,456 8,650              
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 11,377 11,801                
IBNR reserves carried $ 87                  
Cumulative number of reported claims 7,281                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 10,869 10,573                
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,926                  
IBNR reserves carried $ (221)                  
Cumulative number of reported claims 7,359                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 8,760                  
Auto Physical Damage [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 223,513                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 222,826                  
All outstanding liabilities before 2008, net of reinsurance (33)                  
Liability for losses and settlement expenses, net of reinsurance 654                  
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 17,541 17,540 17,558 17,562 17,567 17,578 17,584 17,598 17,743 19,589
IBNR reserves carried $ (9)                  
Cumulative number of reported claims 28,635                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 17,550 17,555 17,557 17,560 17,564 17,577 17,570 17,577 17,662 16,491
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 16,590 16,587 16,602 16,605 16,593 16,639 16,720 16,744 18,077  
IBNR reserves carried $ (11)                  
Cumulative number of reported claims 29,424                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,599 16,601 16,602 16,603 16,592 16,636 16,687 16,661 15,566  
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 18,494 18,488 18,532 18,527 18,549 18,538 18,657 19,249    
IBNR reserves carried $ (28)                  
Cumulative number of reported claims 31,518                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 18,521 18,521 18,528 18,523 18,540 18,529 18,557 17,113    
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 20,867 20,877 20,915 20,917 20,919 21,003 21,965      
IBNR reserves carried $ (27)                  
Cumulative number of reported claims 34,394                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 20,892 20,900 20,912 20,904 20,912 20,984 19,849      
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 21,184 21,161 21,233 21,263 21,342 21,389        
IBNR reserves carried $ (30)                  
Cumulative number of reported claims 31,099                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 21,216 21,216 21,227 21,256 21,328 19,719        
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 22,408 22,371 22,486 22,553 22,847          
IBNR reserves carried $ (4)                  
Cumulative number of reported claims 31,041                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 22,408 22,417 22,463 22,512 20,774          
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 23,946 23,904 24,115 24,897            
IBNR reserves carried $ (51)                  
Cumulative number of reported claims 31,580                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 23,978 23,987 24,110 22,743            
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 26,331 26,612 27,950              
IBNR reserves carried $ (10)                  
Cumulative number of reported claims 30,665                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 26,327 26,538 24,483              
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 27,629 28,070                
IBNR reserves carried $ (310)                  
Cumulative number of reported claims 30,715                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 27,883 26,871                
Auto Physical Damage [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 28,523                  
IBNR reserves carried $ (1,868)                  
Cumulative number of reported claims 29,755                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 27,452                  
Assumed Pro Rata [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 259,193                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 206,153                  
All outstanding liabilities before 2008, net of reinsurance 2,599                  
Liability for losses and settlement expenses, net of reinsurance 55,639                  
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 24,084 24,126 24,068 23,914 24,103 23,972 24,473 24,129 25,463 29,931
IBNR reserves carried 261                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 23,476 23,395 23,253 22,950 22,700 22,284 21,744 20,525 18,268 9,263
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 17,183 17,204 17,212 17,274 17,447 17,626 18,442 19,364 23,812  
IBNR reserves carried 225                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 16,748 16,651 16,463 16,283 16,024 15,481 14,644 13,004 6,105  
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 15,533 15,539 15,589 15,807 15,993 16,658 17,279 19,629    
IBNR reserves carried 135                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 15,299 15,254 15,212 15,172 14,499 14,081 12,057 5,059    
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 28,339 28,440 28,459 29,075 29,848 30,316 30,231      
IBNR reserves carried 182                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 28,037 27,973 27,901 27,477 26,733 23,008 10,220      
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 17,644 17,855 18,429 21,110 21,580 22,113        
IBNR reserves carried 349                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 16,852 16,772 16,403 15,159 12,826 4,478        
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 25,442 26,936 27,545 30,174 23,306          
IBNR reserves carried 1,883                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 21,864 21,123 17,963 12,639 3,886          
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 26,419 28,007 27,776 31,516            
IBNR reserves carried 753                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 23,567 20,745 16,185 6,052            
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 35,148 35,356 38,442              
IBNR reserves carried 1,704                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 30,356 22,042 9,569              
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 39,412 35,830                
IBNR reserves carried 7,664                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 22,280 9,673                
Assumed Pro Rata [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 29,989                  
IBNR reserves carried 14,704                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 7,674                  
Assumed Excess of Loss [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 532,118                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 387,584                  
All outstanding liabilities before 2008, net of reinsurance 18,772                  
Liability for losses and settlement expenses, net of reinsurance 163,306                  
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 37,786 36,928 37,063 37,519 39,606 39,019 40,162 41,427 39,939 43,963
IBNR reserves carried 1,384                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 33,837 33,660 33,216 32,784 32,634 31,320 30,690 28,756 25,556 $ 14,314
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 26,922 27,142 27,913 28,233 30,167 30,518 29,987 30,552 38,903  
IBNR reserves carried 1,496                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 23,264 23,032 22,854 22,231 21,882 21,011 18,803 15,896 $ 8,554  
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 39,166 39,628 40,432 39,675 40,307 40,820 41,011 47,426    
IBNR reserves carried 1,857                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 35,646 35,387 33,709 32,700 30,858 28,037 24,759 $ 9,282    
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 58,279 58,700 59,090 59,345 60,948 61,787 72,124      
IBNR reserves carried 1,977                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 54,628 53,906 52,611 50,613 47,965 42,214 $ 25,309      
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 52,003 52,896 53,247 54,494 56,119 58,852        
IBNR reserves carried 2,898                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 46,735 45,174 43,637 40,641 36,266 $ 21,320        
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 44,829 44,947 45,103 47,705 52,699          
IBNR reserves carried 3,188                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 39,520 37,717 33,422 27,635 $ 11,732          
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 62,009 60,454 59,108 65,573            
IBNR reserves carried 5,061                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 50,242 46,163 39,361 $ 22,172            
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 51,924 55,190 60,183              
IBNR reserves carried 6,372                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 36,918 30,495 $ 13,434              
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 67,206 66,995                
IBNR reserves carried 9,099                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 38,913 $ 18,408                
Assumed Excess of Loss [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 91,994                  
IBNR reserves carried 29,426                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 27,881