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RESERVE FOR LOSSES AND LOSS EXPENSES - Incurred claims and allocated claim adjustment expenses, net of reinsurance (Details)
$ in Thousands
Dec. 31, 2017
USD ($)
claim
Dec. 31, 2016
USD ($)
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 ($)
Dec. 31, 2008
USD ($)
Aviabel                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 68,371                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 25,237                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 93,608                  
Aviabel | Accident Year 2008                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 998                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 (293)                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 705                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 30                  
Cumulative Number of Reported Claims | claim 1,066                  
Aviabel | Accident Year 2009                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 842                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 82                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 924                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 25                  
Cumulative Number of Reported Claims | claim 1,347                  
Aviabel | Accident Year 2010                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 1,516                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 (39)                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,477                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 46                  
Cumulative Number of Reported Claims | claim 1,452                  
Aviabel | Accident Year 2011                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 1,418                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 (423)                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 995                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 43                  
Cumulative Number of Reported Claims | claim 1,420                  
Aviabel | Accident Year 2012                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 5,248                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 (1,066)                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 4,183                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 177                  
Cumulative Number of Reported Claims | claim 1,380                  
Aviabel | Accident Year 2013                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 5,702                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 956                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 6,658                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 200                  
Cumulative Number of Reported Claims | claim 1,286                  
Aviabel | Accident Year 2014                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 10,589                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 (1,636)                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 8,953                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 804                  
Cumulative Number of Reported Claims | claim 1,373                  
Aviabel | Accident Year 2015                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 15,004                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 (1,575)                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 13,429                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 1,650                  
Cumulative Number of Reported Claims | claim 1,475                  
Aviabel | Accident Year 2016                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 19,388                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 2,134                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 21,522                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 4,278                  
Cumulative Number of Reported Claims | claim 1,535                  
Aviabel | Accident Year 2017                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 7,666                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 27,096                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 34,762                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 7,180                  
Cumulative Number of Reported Claims | claim 1,114                  
Novae                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date $ 1,202,130                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 135,493                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,337,624                  
Novae | Accident Year 2008                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 20,515                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 20,515                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 3,552                  
Novae | Accident Year 2009                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 25,486                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 25,486                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 714                  
Novae | Accident Year 2010                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 23,308                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 23,308                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 2,781                  
Novae | Accident Year 2011                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 59,648                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 59,648                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 11,204                  
Novae | Accident Year 2012                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 87,292                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 87,292                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 8,695                  
Novae | Accident Year 2013                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 76,786                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 76,786                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 12,504                  
Novae | Accident Year 2014                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 123,955                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 123,955                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 17,024                  
Novae | Accident Year 2015                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 184,606                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 184,606                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 36,619                  
Novae | Accident Year 2016                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 307,014                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 0                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 307,014                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 54,356                  
Novae | Accident Year 2017                    
Claims Development [Line Items]                    
Net claim and allocated claim adjustment expense reserves at the Acquisition Date 293,520                  
Net incurred claims and allocated claim adjustment expenses from the Acquisition Date to December 31, 2017 135,493                  
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 429,013                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 222,330                  
Insurance | Property and Other                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 3,807,431                  
Insurance | Property and Other | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 216,806 $ 217,846 $ 218,851 $ 220,616 $ 225,007 $ 226,472 $ 242,139 $ 251,722 $ 260,206 $ 312,164
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 982                  
Cumulative Number of Reported Claims | claim 1,573                  
Insurance | Property and Other | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 78,623 78,368 78,720 78,501 80,718 82,683 89,993 99,367 117,662  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 971                  
Cumulative Number of Reported Claims | claim 1,483                  
Insurance | Property and Other | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 115,289 115,740 116,020 116,888 122,472 147,881 155,343 175,554    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 687                  
Cumulative Number of Reported Claims | claim 2,310                  
Insurance | Property and Other | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 309,638 309,197 310,404 313,281 333,911 356,524 380,921      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 2,836                  
Cumulative Number of Reported Claims | claim 3,737                  
Insurance | Property and Other | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 418,869 424,475 428,524 448,763 472,088 461,790        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 9,739                  
Cumulative Number of Reported Claims | claim 27,701                  
Insurance | Property and Other | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 380,800 381,550 387,093 414,394 419,392          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 6,117                  
Cumulative Number of Reported Claims | claim 51,238                  
Insurance | Property and Other | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 417,691 436,130 459,996 463,732            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 6,539                  
Cumulative Number of Reported Claims | claim 60,151                  
Insurance | Property and Other | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 355,883 373,071 373,256              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 12,284                  
Cumulative Number of Reported Claims | claim 43,790                  
Insurance | Property and Other | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 574,267 523,086                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 40,961                  
Cumulative Number of Reported Claims | claim 66,488                  
Insurance | Property and Other | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 939,565                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 333,630                  
Cumulative Number of Reported Claims | claim 237,332                  
Insurance | Marine                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 741,224                  
Insurance | Marine | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 82,848 82,789 83,051 83,432 87,201 93,587 100,793 101,872 106,731 99,618
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 381                  
Cumulative Number of Reported Claims | claim 516                  
Insurance | Marine | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 52,428 52,523 53,622 55,027 57,213 64,601 69,932 74,298 80,665  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 528                  
Cumulative Number of Reported Claims | claim 477                  
Insurance | Marine | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 45,785 47,397 48,823 51,663 53,574 66,639 70,685 68,603    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 735                  
Cumulative Number of Reported Claims | claim 472                  
Insurance | Marine | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 68,008 65,919 65,707 65,697 72,463 78,611 90,659      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 1,549                  
Cumulative Number of Reported Claims | claim 603                  
Insurance | Marine | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 74,541 71,917 70,942 68,842 82,729 89,703        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 12,824                  
Cumulative Number of Reported Claims | claim 700                  
Insurance | Marine | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 83,064 97,777 96,722 101,276 80,034          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 4,121                  
Cumulative Number of Reported Claims | claim 733                  
Insurance | Marine | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 44,439 48,471 44,562 59,665            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 7,167                  
Cumulative Number of Reported Claims | claim 799                  
Insurance | Marine | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 136,608 139,931 158,697              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 16,023                  
Cumulative Number of Reported Claims | claim 915                  
Insurance | Marine | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 78,864 86,324                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 19,460                  
Cumulative Number of Reported Claims | claim 1,372                  
Insurance | Marine | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 74,639                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 48,739                  
Cumulative Number of Reported Claims | claim 1,772                  
Insurance | Aviation                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 169,650                  
Insurance | Aviation | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 5,905 5,996 5,851 5,937 7,108 8,256 8,354 8,516 12,021 14,485
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 42                  
Cumulative Number of Reported Claims | claim 187                  
Insurance | Aviation | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 14,388 14,661 15,494 16,674 16,974 18,146 18,800 14,608 17,505  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 68                  
Cumulative Number of Reported Claims | claim 317                  
Insurance | Aviation | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 8,574 8,784 8,739 8,807 9,791 11,460 11,729 12,939    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 131                  
Cumulative Number of Reported Claims | claim 521                  
Insurance | Aviation | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 7,257 7,290 8,437 9,568 12,791 15,400 17,725      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 218                  
Cumulative Number of Reported Claims | claim 734                  
Insurance | Aviation | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 7,730 7,775 8,724 10,807 10,681 12,788        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 320                  
Cumulative Number of Reported Claims | claim 874                  
Insurance | Aviation | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 15,579 15,264 15,221 16,344 15,656          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 542                  
Cumulative Number of Reported Claims | claim 1,027                  
Insurance | Aviation | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 21,859 24,368 23,046 20,437            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 982                  
Cumulative Number of Reported Claims | claim 1,324                  
Insurance | Aviation | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 29,965 28,512 29,772              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 2,646                  
Cumulative Number of Reported Claims | claim 1,917                  
Insurance | Aviation | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 33,641 29,178                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 5,145                  
Cumulative Number of Reported Claims | claim 1,692                  
Insurance | Aviation | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 24,752                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 12,737                  
Cumulative Number of Reported Claims | claim 1,177                  
Insurance | Credit and Political Risk                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 684,497                  
Insurance | Credit and Political Risk | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 44,408 44,410 45,200 45,600 45,551 45,551 45,554 48,715 63,552 52,993
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 0                  
Cumulative Number of Reported Claims | claim 9                  
Insurance | Credit and Political Risk | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 339,558 339,595 335,315 335,295 335,435 335,558 326,037 305,292 248,084  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 2,040                  
Cumulative Number of Reported Claims | claim 24                  
Insurance | Credit and Political Risk | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 90,885 72,105 65,015 64,981 65,598 63,259 63,179 62,415    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 13,200                  
Cumulative Number of Reported Claims | claim 6                  
Insurance | Credit and Political Risk | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 33,604 45,036 48,333 48,361 47,706 48,665 58,154      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 5,973                  
Cumulative Number of Reported Claims | claim 4                  
Insurance | Credit and Political Risk | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 47 10,322 12,447 12,435 15,672 32,602        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 5                  
Cumulative Number of Reported Claims | claim 4                  
Insurance | Credit and Political Risk | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 14,941 9,880 9,759 25,684 26,439          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 6,662                  
Cumulative Number of Reported Claims | claim 1                  
Insurance | Credit and Political Risk | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 68,321 67,109 70,713 38,825            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 10,466                  
Cumulative Number of Reported Claims | claim 6                  
Insurance | Credit and Political Risk | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 27,513 30,368 30,329              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 4,215                  
Cumulative Number of Reported Claims | claim 2                  
Insurance | Credit and Political Risk | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 43,983 47,250                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 20,194                  
Cumulative Number of Reported Claims | claim 1                  
Insurance | Credit and Political Risk | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 21,237                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 17,958                  
Cumulative Number of Reported Claims | claim 2                  
Insurance | Professional Lines                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 3,270,275                  
Insurance | Professional Lines | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 325,573 326,192 327,240 329,458 309,642 296,499 298,905 280,842 278,691 238,550
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 9,175                  
Cumulative Number of Reported Claims | claim 4,558                  
Insurance | Professional Lines | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 223,737 215,732 239,428 238,902 256,295 245,319 244,751 244,150 240,818  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 13,584                  
Cumulative Number of Reported Claims | claim 5,882                  
Insurance | Professional Lines | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 168,632 181,232 158,946 182,713 205,801 234,334 236,578 231,232    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 26,396                  
Cumulative Number of Reported Claims | claim 5,669                  
Insurance | Professional Lines | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 352,406 343,782 330,562 326,255 333,321 315,654 313,858      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 50,239                  
Cumulative Number of Reported Claims | claim 7,211                  
Insurance | Professional Lines | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 366,725 364,423 376,604 377,277 375,557 329,769        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 70,219                  
Cumulative Number of Reported Claims | claim 8,279                  
Insurance | Professional Lines | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 355,777 365,818 398,578 397,852 384,755          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 95,220                  
Cumulative Number of Reported Claims | claim 9,371                  
Insurance | Professional Lines | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 394,470 423,087 412,288 411,690            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 157,747                  
Cumulative Number of Reported Claims | claim 9,650                  
Insurance | Professional Lines | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 383,959 377,725 377,652              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 186,383                  
Cumulative Number of Reported Claims | claim 9,862                  
Insurance | Professional Lines | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 352,414 349,268                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 220,770                  
Cumulative Number of Reported Claims | claim 10,728                  
Insurance | Professional Lines | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 346,582                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 302,135                  
Cumulative Number of Reported Claims | claim 9,984                  
Insurance | Liability                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 1,085,670                  
Insurance | Liability | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 94,165 108,189 102,444 101,589 81,949 82,225 81,785 80,947 79,836 82,969
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 11,783                  
Cumulative Number of Reported Claims | claim 3,790                  
Insurance | Liability | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 98,999 98,384 101,180 83,282 76,431 67,869 67,410 64,017 61,469  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 10,895                  
Cumulative Number of Reported Claims | claim 2,777                  
Insurance | Liability | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 104,296 105,145 98,086 99,596 98,134 98,648 94,231 79,401    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 12,681                  
Cumulative Number of Reported Claims | claim 2,206                  
Insurance | Liability | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 82,128 83,731 85,243 87,060 83,118 75,329 72,584      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 19,227                  
Cumulative Number of Reported Claims | claim 1,788                  
Insurance | Liability | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 75,342 68,181 70,770 73,282 70,645 70,877        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 27,824                  
Cumulative Number of Reported Claims | claim 1,240                  
Insurance | Liability | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 93,221 87,502 94,258 94,182 92,153          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 24,296                  
Cumulative Number of Reported Claims | claim 1,562                  
Insurance | Liability | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 130,035 128,568 122,686 106,166            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 41,151                  
Cumulative Number of Reported Claims | claim 2,440                  
Insurance | Liability | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 136,615 126,047 127,321              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 61,944                  
Cumulative Number of Reported Claims | claim 3,317                  
Insurance | Liability | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 129,225 123,259                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 90,482                  
Cumulative Number of Reported Claims | claim 3,811                  
Insurance | Liability | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 141,644                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 129,373                  
Cumulative Number of Reported Claims | claim 2,519                  
Reinsurance | Property and Other                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance $ 5,251,457                  
Reinsurance | Property and Other | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 523,591 523,154 524,422 529,918 546,034 557,060 571,142 593,015 577,309 677,556
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims (224)                  
Reinsurance | Property and Other | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 202,300 205,145 203,261 209,335 230,351 237,339 250,630 288,510 344,543  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 1,018                  
Reinsurance | Property and Other | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 581,616 583,563 591,331 597,427 594,238 580,601 610,563 619,241    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 4,587                  
Reinsurance | Property and Other | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,020,771 1,022,452 1,047,944 1,064,864 1,105,415 1,105,962 1,092,977      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 8,207                  
Reinsurance | Property and Other | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 394,332 399,193 415,327 445,932 456,173 488,776        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 6,544                  
Reinsurance | Property and Other | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 397,673 403,217 422,160 452,433 475,162          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 4,083                  
Reinsurance | Property and Other | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 438,815 448,887 461,961 441,147            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 45,519                  
Reinsurance | Property and Other | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 369,734 368,320 386,614              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 27,033                  
Reinsurance | Property and Other | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 452,169 452,342                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 96,090                  
Reinsurance | Property and Other | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 870,456                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 488,104                  
Reinsurance | Professional Lines                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,948,434                  
Reinsurance | Professional Lines | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 169,515 172,937 173,217 174,286 173,316 176,767 178,530 182,587 183,064 176,166
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 6,938                  
Reinsurance | Professional Lines | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 181,665 190,811 194,753 209,625 210,084 219,447 216,737 212,046 212,285  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 11,657                  
Reinsurance | Professional Lines | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 180,219 189,880 197,548 215,043 215,298 212,359 211,397 211,273    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 24,929                  
Reinsurance | Professional Lines | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 201,077 208,973 209,837 212,439 203,706 202,676 202,504      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 51,009                  
Reinsurance | Professional Lines | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 213,601 223,492 224,737 222,600 217,184 210,612        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 75,647                  
Reinsurance | Professional Lines | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 214,477 214,855 216,528 215,425 210,196          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 101,607                  
Reinsurance | Professional Lines | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 219,968 219,960 219,966 219,927            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 85,643                  
Reinsurance | Professional Lines | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 215,178 212,852 212,536              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 124,029                  
Reinsurance | Professional Lines | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 196,852 195,527                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 140,194                  
Reinsurance | Professional Lines | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 155,882                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 144,098                  
Reinsurance | Credit and Surety                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,243,697                  
Reinsurance | Credit and Surety | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 98,714 100,277 100,674 101,903 105,698 106,950 105,765 107,787 116,362 87,400
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 1,231                  
Reinsurance | Credit and Surety | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 96,783 98,469 98,845 102,079 108,149 108,442 109,211 125,656 147,192  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 1,874                  
Reinsurance | Credit and Surety | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 78,645 80,680 82,003 89,657 93,648 96,821 103,332 121,893    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 5,222                  
Reinsurance | Credit and Surety | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 104,997 106,804 115,523 117,586 110,294 112,031 124,030      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 7,464                  
Reinsurance | Credit and Surety | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 135,845 144,084 152,678 155,634 152,873 163,535        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 11,848                  
Reinsurance | Credit and Surety | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 139,679 144,095 148,080 157,311 168,361          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 17,857                  
Reinsurance | Credit and Surety | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 142,909 146,647 139,449 138,056            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 27,627                  
Reinsurance | Credit and Surety | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 165,822 170,980 163,467              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 36,473                  
Reinsurance | Credit and Surety | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 144,741 144,583                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 50,815                  
Reinsurance | Credit and Surety | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 135,562                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 74,667                  
Reinsurance | Motor                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,713,131                  
Reinsurance | Motor | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 62,557 61,702 65,983 72,330 77,027 77,937 80,897 78,193 78,924 74,058
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 20,916                  
Reinsurance | Motor | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 84,458 82,093 87,995 97,089 96,069 93,917 91,915 83,784 85,779  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 21,053                  
Reinsurance | Motor | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 87,253 90,839 100,707 106,058 112,285 113,304 112,528 103,990    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 24,419                  
Reinsurance | Motor | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 150,818 161,958 171,007 175,021 168,734 164,579 160,444      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 33,732                  
Reinsurance | Motor | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 141,923 151,820 156,957 164,734 176,870 186,033        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 25,982                  
Reinsurance | Motor | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 143,186 146,799 156,692 168,554 169,876          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 26,041                  
Reinsurance | Motor | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 185,570 188,725 193,691 190,363            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 24,003                  
Reinsurance | Motor | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 233,172 229,110 231,614              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 37,198                  
Reinsurance | Motor | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 276,126 255,354                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 55,173                  
Reinsurance | Motor | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 348,068                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 170,065                  
Reinsurance | Liability                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 1,912,565                  
Reinsurance | Liability | Accident Year 2008                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 86,008 95,649 106,942 111,873 133,917 139,564 141,553 141,152 140,460 $ 140,069
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 10,016                  
Reinsurance | Liability | Accident Year 2009                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 171,979 181,488 195,679 208,301 188,090 180,596 182,970 176,187 $ 175,100  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 23,215                  
Reinsurance | Liability | Accident Year 2010                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 166,533 182,794 192,051 202,649 184,180 183,773 172,261 $ 173,358    
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 29,101                  
Reinsurance | Liability | Accident Year 2011                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 196,277 196,948 200,190 193,228 175,279 173,815 $ 174,125      
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 34,097                  
Reinsurance | Liability | Accident Year 2012                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 172,124 174,765 173,596 168,956 164,742 $ 168,641        
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 43,129                  
Reinsurance | Liability | Accident Year 2013                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 185,321 185,689 183,683 177,606 $ 173,966          
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 71,652                  
Reinsurance | Liability | Accident Year 2014                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 202,130 206,100 204,323 $ 201,355            
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 91,483                  
Reinsurance | Liability | Accident Year 2015                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 217,480 216,518 $ 216,076              
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 125,377                  
Reinsurance | Liability | Accident Year 2016                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 247,768 $ 241,952                
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims 171,869                  
Reinsurance | Liability | Accident Year 2017                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance 266,945                  
Total of Incurred-But-Not-Reported Liabilities Plus Expected Development on Reported Claims $ 226,036