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LIABILITY FOR LOSSES AND SETTLEMENT EXPENSES SHORT-DURATION INSURANCE CONTRACTS DEVELOPMENT TABLES (Details)
$ in Thousands
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 ($)
Dec. 31, 2009
USD ($)
Claims development [Line Items]                    
Liability for losses and settlement expenses, net of reinsurance $ 716,495                  
Commercial Auto Liability [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 470,241                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 349,805                  
All outstanding liabilities before 2009, net of reinsurance (38)                  
Liability for losses and settlement expenses, net of reinsurance 120,398                  
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 24,677 $ 24,697 $ 24,655 $ 24,730 $ 24,874 $ 24,986 $ 25,370 $ 26,667 $ 27,923 $ 28,973
IBNR reserves carried $ 0                  
Cumulative number of reported claims 10,482                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 24,634 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 26,159 26,166 26,166 26,479 26,252 26,401 26,478 27,480 30,377  
IBNR reserves carried $ 2                  
Cumulative number of reported claims 11,393                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 26,105 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 31,286 31,638 31,635 31,914 31,961 31,098 29,790 32,775    
IBNR reserves carried $ 0                  
Cumulative number of reported claims 11,768                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 31,146 30,878 30,293 29,121 26,598 22,206 14,875 6,801    
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 37,739 37,753 37,693 37,681 37,098 34,235 32,768      
IBNR reserves carried $ 7                  
Cumulative number of reported claims 11,943                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 37,125 36,541 35,406 32,636 26,023 19,398 8,830      
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 43,328 43,159 42,336 42,086 40,382 37,265        
IBNR reserves carried $ 20                  
Cumulative number of reported claims 13,640                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 42,364 40,807 36,232 29,997 19,975 8,729        
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 51,491 51,933 51,455 49,998 50,342          
IBNR reserves carried $ 390                  
Cumulative number of reported claims 15,071                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 48,467 44,783 37,433 25,746 12,069          
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 59,054 58,627 57,824 53,883            
IBNR reserves carried $ 919                  
Cumulative number of reported claims 16,541                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 50,675 39,478 27,424 13,336            
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 62,051 61,188 59,468              
IBNR reserves carried $ 3,451                  
Cumulative number of reported claims 16,978                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 43,169 30,233 13,583              
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 64,187 63,909                
IBNR reserves carried $ 9,011                  
Cumulative number of reported claims 16,468                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 31,056 14,474                
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 70,269                  
IBNR reserves carried $ 22,856                  
Cumulative number of reported claims 15,759                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 15,064                  
Commercial Property [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 524,692                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 494,504                  
All outstanding liabilities before 2009, net of reinsurance 25                  
Liability for losses and settlement expenses, net of reinsurance 30,213                  
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 36,351 36,292 36,020 36,056 35,926 35,622 35,881 35,985 36,003 39,511
IBNR reserves carried $ 0                  
Cumulative number of reported claims 14,657                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 36,246 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 39,423 39,347 39,428 39,379 39,154 39,071 38,770 38,650 40,422  
IBNR reserves carried $ 1                  
Cumulative number of reported claims 16,278                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,368 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 58,122 58,148 58,375 57,703 57,629 57,271 57,614 58,930    
IBNR reserves carried $ 0                  
Cumulative number of reported claims 19,511                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 58,116 58,106 57,607 57,065 56,249 54,803 53,226 41,524    
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 46,880 46,750 46,566 46,273 45,313 44,157 41,535      
IBNR reserves carried $ (8)                  
Cumulative number of reported claims 16,072                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 46,708 46,562 46,270 44,543 43,628 41,862 32,879      
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 52,432 52,966 53,070 52,511 50,976 50,266        
IBNR reserves carried $ (15)                  
Cumulative number of reported claims 16,012                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 52,266 52,182 51,457 50,460 47,683 36,555        
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 60,250 60,867 60,662 60,990 60,018          
IBNR reserves carried $ 38                  
Cumulative number of reported claims 16,755                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 59,815 59,255 58,045 55,679 43,022          
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 55,027 55,659 56,798 55,508            
IBNR reserves carried $ (110)                  
Cumulative number of reported claims 14,403                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 53,405 52,444 50,068 37,208            
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 58,227 58,343 59,708              
IBNR reserves carried $ (91)                  
Cumulative number of reported claims 14,978                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 54,681 51,103 41,652              
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 54,357 55,459                
IBNR reserves carried $ (122)                  
Cumulative number of reported claims 15,006                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 50,280 38,114                
Commercial Property [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 63,623                  
IBNR reserves carried $ 2,353                  
Cumulative number of reported claims 12,946                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 43,619                  
Workers' Compensation [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 484,471                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 374,035                  
All outstanding liabilities before 2009, net of reinsurance 34,313                  
Liability for losses and settlement expenses, net of reinsurance 144,749                  
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 43,217 43,417 42,774 43,724 43,590 44,093 44,041 44,098 43,335 46,130
IBNR reserves carried $ 1,443                  
Cumulative number of reported claims 19,242                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 40,223 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 48,884 49,435 49,145 50,069 49,851 49,906 50,057 49,336 46,328  
IBNR reserves carried $ 1,822                  
Cumulative number of reported claims 19,631                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 44,669 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 44,070 44,056 43,695 44,427 44,506 44,709 46,724 47,836    
IBNR reserves carried $ 1,948                  
Cumulative number of reported claims 19,574                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,652 39,167 38,437 37,027 35,295 32,237 26,291 13,291    
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 45,402 45,276 45,088 46,928 47,756 50,094 51,099      
IBNR reserves carried $ 1,836                  
Cumulative number of reported claims 19,395                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 41,092 40,292 39,456 37,307 33,943 28,109 14,015      
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 45,910 45,949 46,102 48,946 51,637 52,141        
IBNR reserves carried $ 2,290                  
Cumulative number of reported claims 19,866                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 40,061 39,254 37,907 35,061 29,219 14,917        
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 46,722 47,836 47,472 50,973 51,515          
IBNR reserves carried $ 2,190                  
Cumulative number of reported claims 19,473                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 40,941 39,046 35,883 28,894 14,692          
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 47,755 47,227 48,919 54,960            
IBNR reserves carried $ 2,335                  
Cumulative number of reported claims 19,227                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 39,310 35,458 29,023 14,956            
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 47,719 48,276 57,832              
IBNR reserves carried $ 2,418                  
Cumulative number of reported claims 20,325                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 35,778 29,592 15,473              
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 55,312 52,409                
IBNR reserves carried $ 3,938                  
Cumulative number of reported claims 22,061                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 33,234 16,863                
Workers' Compensation [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 59,480                  
IBNR reserves carried $ 6,828                  
Cumulative number of reported claims 21,734                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 19,075                  
Other Liability [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 441,406                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 279,430                  
All outstanding liabilities before 2009, net of reinsurance 12,100                  
Liability for losses and settlement expenses, net of reinsurance 174,076                  
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 31,739 32,063 32,521 32,384 32,827 35,614 34,263 37,650 39,908 44,497
IBNR reserves carried $ 115                  
Cumulative number of reported claims 9,855                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 30,993 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 33,359 33,736 34,556 34,655 36,137 38,829 34,655 36,213 41,624  
IBNR reserves carried $ 449                  
Cumulative number of reported claims 10,155                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 32,083 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 31,346 31,711 32,452 33,649 35,177 35,125 42,982 44,490    
IBNR reserves carried $ 400                  
Cumulative number of reported claims 10,011                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 29,608 29,060 28,228 25,647 22,154 17,308 10,572 4,730    
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 38,050 37,180 37,093 40,275 41,139 42,081 42,661      
IBNR reserves carried $ 668                  
Cumulative number of reported claims 10,073                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 35,903 32,753 29,651 25,095 19,661 12,851 4,720      
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 37,055 39,175 42,187 42,544 43,837 47,974        
IBNR reserves carried $ 1,219                  
Cumulative number of reported claims 10,616                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 33,350 31,752 27,642 21,122 11,894 4,414        
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 50,950 51,047 52,601 54,403 61,382          
IBNR reserves carried $ 2,214                  
Cumulative number of reported claims 10,966                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 40,036 35,318 27,506 17,267 5,630          
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 40,300 43,379 47,553 54,221            
IBNR reserves carried $ 3,048                  
Cumulative number of reported claims 10,709                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 26,309 19,022 11,588 4,331            
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 57,388 56,384 59,052              
IBNR reserves carried $ 9,177                  
Cumulative number of reported claims 10,708                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 28,638 18,784 6,403              
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 57,714 59,420                
IBNR reserves carried $ 13,844                  
Cumulative number of reported claims 10,032                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,555 6,322                
Other Liability [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 63,505                  
IBNR reserves carried $ 27,373                  
Cumulative number of reported claims 9,852                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 5,955                  
Personal Auto Liability [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 87,027                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 81,403                  
All outstanding liabilities before 2009, net of reinsurance 8                  
Liability for losses and settlement expenses, net of reinsurance 5,632                  
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 9,311 9,312 9,325 9,339 9,382 9,353 9,386 9,452 9,653 10,168
IBNR reserves carried $ (1)                  
Cumulative number of reported claims 7,524                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,313 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,638 9,649 9,676 9,656 9,700 9,698 9,736 9,851 9,815  
IBNR reserves carried $ (1)                  
Cumulative number of reported claims 7,438                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,636 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,365 9,413 9,311 9,460 9,432 9,331 9,388 9,741    
IBNR reserves carried $ (2)                  
Cumulative number of reported claims 8,052                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,367 9,335 9,153 9,038 8,883 8,129 6,842 3,950    
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 10,610 10,626 10,537 10,731 11,023 10,756 10,917      
IBNR reserves carried $ (3)                  
Cumulative number of reported claims 7,875                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 10,565 10,415 10,244 9,871 9,091 7,439 4,779      
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 10,060 10,085 10,085 10,376 10,384 10,492        
IBNR reserves carried $ (1)                  
Cumulative number of reported claims 7,237                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 10,021 9,932 9,648 8,985 7,521 4,377        
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 9,113 9,204 9,331 9,631 10,573          
IBNR reserves carried $ (42)                  
Cumulative number of reported claims 6,316                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 8,992 8,598 7,755 6,392 3,970          
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 8,225 8,378 8,638 9,119            
IBNR reserves carried $ (18)                  
Cumulative number of reported claims 5,670                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 7,975 7,535 6,229 3,800            
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 6,490 6,584 7,404              
IBNR reserves carried $ (1)                  
Cumulative number of reported claims 4,720                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 6,046 5,427 3,505              
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 7,213 7,043                
IBNR reserves carried $ (13)                  
Cumulative number of reported claims 4,728                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 5,735 3,467                
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 7,002                  
IBNR reserves carried $ 487                  
Cumulative number of reported claims 4,687                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 3,753                  
Homeowners Insurance [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 143,633                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 141,911                  
All outstanding liabilities before 2009, net of reinsurance 0                  
Liability for losses and settlement expenses, net of reinsurance 1,722                  
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 16,467 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 16,467 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 17,132 17,139 17,146 17,129 17,093 17,053 17,074 17,523 17,875  
IBNR reserves carried $ 0                  
Cumulative number of reported claims 12,147                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 17,132 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 23,369 23,350 23,415 23,448 23,309 22,975 23,389 24,530    
IBNR reserves carried $ 0                  
Cumulative number of reported claims 14,288                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 23,370 23,368 23,370 23,403 23,136 22,737 22,421 19,828    
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 16,925 16,879 16,892 16,929 16,836 16,496 16,057      
IBNR reserves carried $ 0                  
Cumulative number of reported claims 10,141                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,926 16,905 16,859 16,793 16,582 16,283 13,759      
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 14,757 14,737 14,784 14,685 14,833 14,844        
IBNR reserves carried $ (5)                  
Cumulative number of reported claims 8,688                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 14,741 14,703 14,681 14,621 14,285 11,735        
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 13,332 13,427 13,447 13,328 13,228          
IBNR reserves carried $ (1)                  
Cumulative number of reported claims 7,427                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 13,295 13,269 13,215 13,025 11,065          
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 11,079 11,041 11,153 11,233            
IBNR reserves carried $ (45)                  
Cumulative number of reported claims 5,951                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 10,866 10,730 10,456 8,650            
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 11,397 11,377 11,801              
IBNR reserves carried $ (15)                  
Cumulative number of reported claims 7,318                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 11,243 10,869 10,573              
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,679 9,926                
IBNR reserves carried $ (84)                  
Cumulative number of reported claims 7,803                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 9,696 8,760                
Homeowners Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 9,496                  
IBNR reserves carried $ (302)                  
Cumulative number of reported claims 4,900                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 8,175                  
Auto Physical Damage [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 237,953                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 236,360                  
All outstanding liabilities before 2009, net of reinsurance (3)                  
Liability for losses and settlement expenses, net of reinsurance 1,590                  
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 16,582 16,590 16,587 16,602 16,605 16,593 16,639 16,720 16,744 18,077
IBNR reserves carried $ (17)                  
Cumulative number of reported claims 29,427                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 16,599 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 2009 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 18,497 18,494 18,488 18,532 18,527 18,549 18,538 18,657 19,249  
IBNR reserves carried $ (22)                  
Cumulative number of reported claims 31,523                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 18,518 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 2010 [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 20,859 20,867 20,877 20,915 20,917 20,919 21,003 21,965    
IBNR reserves carried $ (32)                  
Cumulative number of reported claims 34,397                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 20,889 20,892 20,900 20,912 20,904 20,912 20,984 19,849    
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 21,172 21,184 21,161 21,233 21,263 21,342 21,389      
IBNR reserves carried $ (40)                  
Cumulative number of reported claims 31,111                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 21,210 21,216 21,216 21,227 21,256 21,328 19,719      
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 22,353 22,408 22,371 22,486 22,553 22,847        
IBNR reserves carried $ (52)                  
Cumulative number of reported claims 31,042                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 22,403 22,408 22,417 22,463 22,512 20,774        
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 23,899 23,946 23,904 24,115 24,897          
IBNR reserves carried $ (75)                  
Cumulative number of reported claims 31,585                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 23,972 23,978 23,987 24,110 22,743          
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 26,224 26,331 26,612 27,950            
IBNR reserves carried $ (96)                  
Cumulative number of reported claims 30,672                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 26,308 26,327 26,538 24,483            
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 27,595 27,629 28,070              
IBNR reserves carried $ (158)                  
Cumulative number of reported claims 30,752                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 27,742 27,883 26,871              
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 28,589 28,523                
IBNR reserves carried $ (393)                  
Cumulative number of reported claims 31,486                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 29,050 27,452                
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 32,183                  
IBNR reserves carried $ (567)                  
Cumulative number of reported claims 30,307                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 29,669                  
Assumed Pro Rata [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 260,213                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 210,756                  
All outstanding liabilities before 2009, net of reinsurance 2,648                  
Liability for losses and settlement expenses, net of reinsurance 52,105                  
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 16,993 17,059 17,080 17,088 17,150 17,323 17,496 18,302 19,222 23,731
IBNR reserves carried 173                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 16,654 16,623 16,526 16,338 16,159 15,900 15,364 14,538 12,927 6,073
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 15,313 15,340 15,347 15,396 15,610 15,794 16,456 17,078 19,514  
IBNR reserves carried 95                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 15,138 15,107 15,062 15,021 14,978 14,328 13,924 11,940 5,016  
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 27,800 28,110 28,209 28,228 28,838 29,604 30,057 30,093    
IBNR reserves carried 117                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 27,911 27,810 27,748 27,677 27,270 26,541 22,859 10,178    
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 17,560 17,380 17,592 18,158 20,823 21,282 21,935      
IBNR reserves carried 296                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 16,699 16,598 16,520 16,161 14,935 12,650 4,403      
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 24,428 25,173 26,664 27,260 29,921 23,183        
IBNR reserves carried 1,215                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 22,483 21,601 20,871 17,744 12,491 3,845        
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 26,300 26,160 27,771 27,525 31,262          
IBNR reserves carried 571                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 25,141 23,326 20,534 16,046 5,988          
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 35,748 34,962 35,180 38,311            
IBNR reserves carried 1,049                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 31,552 30,205 21,932 9,531            
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 38,526 39,143 35,696              
IBNR reserves carried 4,568                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 29,786 22,131 9,626              
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 33,856 29,852                
IBNR reserves carried 7,545                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 20,289 7,645                
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 23,689                  
IBNR reserves carried 11,484                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 5,103                  
Assumed Excess of Loss [Member]                    
Claims development [Line Items]                    
Incurred losses and allocated settlement expenses, net of reinsurance 589,741                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 424,299                  
All outstanding liabilities before 2009, net of reinsurance 18,857                  
Liability for losses and settlement expenses, net of reinsurance 184,299                  
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 26,654 26,905 27,125 27,895 28,215 30,150 30,499 29,969 30,534 38,883
IBNR reserves carried 989                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 23,748 23,247 23,015 22,837 22,214 21,865 20,995 18,789 15,885 $ 8,554
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 38,275 39,119 39,581 40,385 39,629 40,260 40,773 40,962 47,396  
IBNR reserves carried 912                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 35,993 35,600 35,341 33,664 32,654 30,813 28,011 24,736 $ 9,282  
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 57,851 58,213 58,632 59,018 59,276 60,873 61,702 72,077    
IBNR reserves carried 1,143                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 55,137 54,562 53,840 52,546 50,549 47,902 42,175 $ 25,313    
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 52,637 51,940 52,834 53,186 54,421 56,024 58,767      
IBNR reserves carried 1,863                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 47,620 46,688 45,127 43,591 40,601 36,232 $ 21,318      
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 43,766 44,541 44,658 44,812 47,375 52,392        
IBNR reserves carried 2,283                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 40,368 39,246 37,467 33,188 27,477 $ 11,695        
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 64,109 61,717 60,144 58,792 65,289          
IBNR reserves carried 4,345                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 54,898 49,974 45,903 39,153 $ 22,160          
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 53,235 51,570 54,788 59,837            
IBNR reserves carried 4,858                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 41,608 36,617 30,273 $ 13,381            
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 65,979 66,645 66,569              
IBNR reserves carried 6,469                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 48,359 38,565 $ 18,303              
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 85,061 91,769                
IBNR reserves carried 7,724                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance 56,197 $ 27,837                
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 102,174                  
IBNR reserves carried 39,651                  
Cumulative paid losses and allocated settlement expenses, net of reinsurance $ 20,371