XML 99 R86.htm IDEA: XBRL DOCUMENT v3.22.0.1
Reserves For Losses And Loss Expenses (Loss and Loss Expenses Incurred, Net of Reinsurance, and Cumulative Paid Claims and Claim Adjustment Expenses, Net of Reinsurance) (Details)
$ in Thousands
Dec. 31, 2021
USD ($)
claim
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Claims Development [Line Items]                    
Reserves for loss and loss adjustment expenses, net of reinsurance $ 13,300,678                  
Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 10,758,937                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 5,927,071                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 117,839                  
Reserves for loss and loss adjustment expenses, net of reinsurance 4,949,705                  
Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 6,520,177                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 4,813,541                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 229,691                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,936,327                  
Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 3,549,028                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 2,068,307                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 24,145                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,504,866                  
Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 4,492,974                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 3,571,330                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 1,869                  
Reserves for loss and loss adjustment expenses, net of reinsurance 923,513                  
Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 7,113,743                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 6,463,178                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 2,523                  
Reserves for loss and loss adjustment expenses, net of reinsurance 653,088                  
Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 3,024,680                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 1,635,708                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 385,481                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,774,453                  
Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 624,829                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 115,159                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 716,077                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,225,747                  
Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,240,697                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 1,015,451                  
Reserves for loss and loss adjustment expenses before 2012, net of reinsurance 2,474                  
Reserves for loss and loss adjustment expenses, net of reinsurance 227,720                  
Accident Year 2011 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 708,031 $ 712,984 $ 714,681 $ 716,643 $ 722,092 $ 711,876 $ 707,937 $ 701,634 $ 700,946 $ 692,236
Cumulative paid claims and claim adjustment expenses, net of reinsurance 673,555 667,147 651,584 621,012 579,062 511,933 416,187 298,293 157,389 57,589
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 16,190                  
Short-duration insurance contract, cumulative number of reported claims | claim 24,000                  
Accident Year 2011 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 504,409 506,827 506,730 508,169 512,707 509,167 503,863 503,956 501,810 501,681
Cumulative paid claims and claim adjustment expenses, net of reinsurance 470,850 466,028 459,119 451,991 437,196 419,588 387,368 339,560 255,063 115,536
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 13,830                  
Short-duration insurance contract, cumulative number of reported claims | claim 48,000                  
Accident Year 2011 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 250,231 249,539 246,731 246,116 247,348 240,785 252,531 267,284 243,987 240,363
Cumulative paid claims and claim adjustment expenses, net of reinsurance 236,972 236,216 233,379 225,186 215,952 191,500 160,044 128,924 87,248 21,895
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 6,098                  
Short-duration insurance contract, cumulative number of reported claims | claim 6,000                  
Accident Year 2011 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 365,910 366,128 365,971 366,704 364,483 364,237 355,609 342,588 326,831 314,309
Cumulative paid claims and claim adjustment expenses, net of reinsurance 363,034 363,073 361,919 360,842 355,786 344,478 312,342 273,446 215,214 136,844
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 218                  
Short-duration insurance contract, cumulative number of reported claims | claim 41,000                  
Accident Year 2011 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 507,683 508,815 508,058 508,988 507,093 508,139 536,151 540,845 539,963 531,725
Cumulative paid claims and claim adjustment expenses, net of reinsurance 506,144 506,095 504,973 504,243 499,978 498,826 518,135 507,382 456,559 282,573
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 801                  
Short-duration insurance contract, cumulative number of reported claims | claim 24,000                  
Accident Year 2011 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 337,124 335,933 332,861 336,201 338,118 333,992 325,045 332,252 337,114 333,116
Cumulative paid claims and claim adjustment expenses, net of reinsurance 282,363 277,926 258,404 242,644 220,821 188,208 153,349 112,036 62,289 22,419
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 11,446                  
Accident Year 2011 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 65,686 66,269 67,205 69,361 67,878 74,061 75,274 73,670 73,230 72,366
Cumulative paid claims and claim adjustment expenses, net of reinsurance 24,365 22,528 20,004 17,982 15,738 13,234 11,167 10,815 6,097 1,127
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 7,617                  
Accident Year 2011 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 89,460 91,078 84,759 84,950 84,020 84,010 85,548 86,525 94,860 103,984
Cumulative paid claims and claim adjustment expenses, net of reinsurance 89,461 88,932 82,745 81,874 79,166 77,604 70,725 64,282 51,802 $ 15,690
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 591                  
Accident Year 2012 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 811,143 809,119 804,919 810,344 803,974 783,020 783,199 791,016 750,501  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 741,756 720,773 694,234 648,699 587,822 472,142 331,309 188,374 63,322  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 29,110                  
Short-duration insurance contract, cumulative number of reported claims | claim 26,000                  
Accident Year 2012 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 538,503 540,322 541,926 542,274 547,000 543,238 546,995 547,295 552,570  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 496,809 489,075 479,104 466,580 447,894 414,160 363,028 277,538 117,900  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 17,768                  
Short-duration insurance contract, cumulative number of reported claims | claim 53,000                  
Accident Year 2012 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 284,610 284,479 286,875 281,652 273,074 251,249 245,263 249,477 271,758  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 271,867 265,007 259,735 250,294 208,123 178,367 120,081 64,245 24,215  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 6,488                  
Short-duration insurance contract, cumulative number of reported claims | claim 7,000                  
Accident Year 2012 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 365,338 365,100 366,165 367,027 367,456 377,050 368,894 349,136 327,514  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 363,505 363,118 362,358 353,623 343,742 322,624 267,253 218,596 142,929  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 731                  
Short-duration insurance contract, cumulative number of reported claims | claim 44,000                  
Accident Year 2012 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 546,765 547,066 547,806 549,728 553,233 554,736 580,445 589,447 579,486  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 543,806 542,378 541,182 540,583 539,324 532,472 539,588 490,363 315,019  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 1,424                  
Short-duration insurance contract, cumulative number of reported claims | claim 25,000                  
Accident Year 2012 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 304,709 303,563 305,290 300,778 295,143 284,710 274,682 271,557 320,581  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 255,948 243,100 227,087 206,595 178,889 144,985 110,735 63,939 28,982  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 14,065                  
Accident Year 2012 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 25,701 29,758 31,752 35,120 38,551 44,162 48,143 50,355 63,995  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 8,805 6,476 5,349 4,418 3,396 3,008 2,158 1,897 647  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 7,609                  
Accident Year 2012 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 106,436 107,669 109,814 112,006 112,687 112,054 114,245 112,805 141,705  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 104,506 104,521 107,721 106,157 104,437 101,651 92,728 74,650 $ 36,620  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 567                  
Accident Year 2013 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 864,787 866,292 871,130 864,965 852,171 847,719 849,690 847,878    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 761,143 731,588 681,278 595,187 481,002 338,740 191,072 79,008    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 51,651                  
Short-duration insurance contract, cumulative number of reported claims | claim 28,000                  
Accident Year 2013 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 602,000 600,194 604,030 615,435 617,242 627,767 637,307 639,436    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 538,914 531,475 521,141 503,915 471,235 412,611 319,743 148,405    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 29,314                  
Short-duration insurance contract, cumulative number of reported claims | claim 57,000                  
Accident Year 2013 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 258,330 258,937 260,106 241,329 245,768 261,937 248,723 255,364    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 238,121 228,815 217,322 200,319 176,915 139,340 84,141 19,584    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 13,311                  
Short-duration insurance contract, cumulative number of reported claims | claim 7,000                  
Accident Year 2013 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 408,640 409,498 413,953 414,105 416,613 418,639 385,302 363,952    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 406,228 405,226 402,524 394,562 365,849 328,589 237,723 155,596    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 394                  
Short-duration insurance contract, cumulative number of reported claims | claim 47,000                  
Accident Year 2013 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 666,738 668,510 666,063 665,820 664,951 666,259 716,253 710,530    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 660,031 659,487 656,913 649,632 634,310 614,832 602,682 373,791    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 1,956                  
Short-duration insurance contract, cumulative number of reported claims | claim 30,000                  
Accident Year 2013 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 339,321 338,190 326,496 326,964 332,730 320,902 321,504 321,644    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 273,024 253,573 228,728 199,109 155,908 116,424 69,248 21,340    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 20,465                  
Accident Year 2013 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 40,652 42,618 42,541 41,671 45,758 49,570 57,650 63,561    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 11,938 11,154 7,595 5,808 4,175 3,354 1,729 377    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 10,922                  
Accident Year 2013 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 97,640 99,572 99,171 99,508 100,255 97,509 96,894 113,373    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 95,523 94,893 93,409 91,701 88,561 82,380 67,041 $ 38,919    
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 1,049                  
Accident Year 2014 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 984,528 977,944 967,764 965,725 962,470 987,552 951,915      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 816,955 758,115 676,714 538,647 382,589 211,030 82,763      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 64,794                  
Short-duration insurance contract, cumulative number of reported claims | claim 27,000                  
Accident Year 2014 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 617,478 620,741 626,432 641,169 650,997 690,525 712,800      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 544,849 531,512 512,933 477,541 421,734 323,744 139,320      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 40,553                  
Short-duration insurance contract, cumulative number of reported claims | claim 58,000                  
Accident Year 2014 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 285,255 284,747 293,558 277,962 276,829 259,868 261,238      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 241,413 234,207 217,238 188,258 140,253 85,761 20,517      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 24,656                  
Short-duration insurance contract, cumulative number of reported claims | claim 8,000                  
Accident Year 2014 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 428,813 431,675 433,227 432,160 423,928 417,771 389,829      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 417,721 411,898 398,423 370,773 325,697 265,766 160,148      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 1,371                  
Short-duration insurance contract, cumulative number of reported claims | claim 53,000                  
Accident Year 2014 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 716,332 718,104 719,612 727,861 729,326 733,145 744,761      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 713,522 706,707 700,867 691,093 669,076 613,338 396,128      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 4,505                  
Short-duration insurance contract, cumulative number of reported claims | claim 32,000                  
Accident Year 2014 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 306,358 304,972 294,804 253,982 231,859 233,204 260,768      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 234,736 206,222 179,308 141,855 91,566 48,628 17,894      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 23,525                  
Accident Year 2014 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 36,774 39,781 39,682 45,115 50,099 57,897 69,977      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 5,421 5,083 4,416 4,099 3,272 2,481 2,069      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 13,941                  
Accident Year 2014 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 130,933 131,342 129,668 130,553 131,963 117,724 127,387      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 127,086 125,663 122,763 118,733 109,217 89,251 $ 53,508      
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 1,157                  
Accident Year 2015 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,062,023 1,046,122 1,032,035 1,020,679 1,011,800 1,018,792        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 767,795 677,852 558,896 390,465 209,118 69,532        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 117,676                  
Short-duration insurance contract, cumulative number of reported claims | claim 28,000                  
Accident Year 2015 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 657,972 651,278 660,520 684,700 696,339 702,716        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 558,934 537,861 504,850 446,072 338,835 142,998        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 46,447                  
Short-duration insurance contract, cumulative number of reported claims | claim 58,000                  
Accident Year 2015 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 470,950 441,535 404,271 363,221 326,427 312,109        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 359,386 299,198 256,725 202,545 103,108 28,783        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 40,227                  
Short-duration insurance contract, cumulative number of reported claims | claim 9,000                  
Accident Year 2015 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 440,819 441,122 444,322 443,275 431,939 432,214        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 421,388 410,843 391,396 342,437 280,373 185,253        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 3,145                  
Short-duration insurance contract, cumulative number of reported claims | claim 52,000                  
Accident Year 2015 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 756,378 753,991 759,531 765,044 778,059 774,764        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 740,703 733,951 728,853 713,506 671,886 417,882        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 5,444                  
Short-duration insurance contract, cumulative number of reported claims | claim 34,000                  
Accident Year 2015 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 303,036 303,385 269,481 246,947 254,415 242,375        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 206,266 172,489 140,897 100,578 61,940 19,939        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 29,111                  
Accident Year 2015 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 65,222 65,485 64,957 71,404 70,281 72,657        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 9,883 7,685 5,928 5,573 4,783 2,498        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 18,607                  
Accident Year 2015 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 184,600 186,605 181,291 182,026 174,793 168,347        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 178,508 176,358 168,884 157,734 133,740 $ 78,994        
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 2,039                  
Accident Year 2016 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,179,982 1,140,112 1,123,297 1,100,790 1,066,950          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 775,705 639,775 453,790 256,176 80,127          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 171,499                  
Short-duration insurance contract, cumulative number of reported claims | claim 27,000                  
Accident Year 2016 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 683,880 673,216 689,622 733,505 762,093          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 559,198 525,753 468,817 362,299 153,456          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 54,759                  
Short-duration insurance contract, cumulative number of reported claims | claim 58,000                  
Accident Year 2016 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 385,450 378,640 339,781 333,657 334,509          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 262,273 244,025 163,454 96,818 36,744          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 70,978                  
Short-duration insurance contract, cumulative number of reported claims | claim 10,000                  
Accident Year 2016 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 440,610 434,717 430,782 428,988 431,059          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 402,422 372,324 327,411 267,859 181,023          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 6,890                  
Short-duration insurance contract, cumulative number of reported claims | claim 47,000                  
Accident Year 2016 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 747,453 747,861 748,516 754,300 754,050          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 735,430 731,588 719,434 690,502 445,934          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 9,657                  
Short-duration insurance contract, cumulative number of reported claims | claim 42,000                  
Accident Year 2016 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 283,323 263,476 240,900 222,888 232,886          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 148,128 124,265 69,844 40,310 16,490          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 48,441                  
Accident Year 2016 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 66,795 71,025 70,749 80,508 76,701          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 18,375 17,327 15,356 12,810 6,282          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 23,023                  
Accident Year 2016 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 192,014 198,251 199,645 200,656 206,795          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 182,799 179,997 171,880 141,484 $ 72,160          
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 2,784                  
Accident Year 2017 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,157,499 1,122,423 1,132,810 1,105,223            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 616,293 436,100 264,541 86,931            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 264,059                  
Short-duration insurance contract, cumulative number of reported claims | claim 27,000                  
Accident Year 2017 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 724,056 715,055 724,697 778,964            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 574,889 508,546 397,464 171,006            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 62,856                  
Short-duration insurance contract, cumulative number of reported claims | claim 56,000                  
Accident Year 2017 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 360,815 334,854 323,759 336,524            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 199,461 155,836 100,087 28,360            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 104,215                  
Short-duration insurance contract, cumulative number of reported claims | claim 10,000                  
Accident Year 2017 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 494,623 479,257 462,821 442,838            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 413,150 350,368 281,707 180,196            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 12,573                  
Short-duration insurance contract, cumulative number of reported claims | claim 46,000                  
Accident Year 2017 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 745,726 747,393 750,095 761,015            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 726,169 709,230 662,714 415,578            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 16,064                  
Short-duration insurance contract, cumulative number of reported claims | claim 48,000                  
Accident Year 2017 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 249,019 232,643 212,101 222,959            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 110,082 77,939 41,213 11,144            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 68,680                  
Accident Year 2017 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 66,180 71,448 72,505 77,820            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 10,359 9,368 8,230 6,141            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 28,214                  
Accident Year 2017 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 105,447 103,386 112,243 108,436            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 88,050 82,509 65,313 $ 34,116            
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 2,904                  
Accident Year 2018 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,239,419 1,238,948 1,242,139              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 471,687 275,680 88,369              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 440,178                  
Short-duration insurance contract, cumulative number of reported claims | claim 27,000                  
Accident Year 2018 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 732,762 721,018 784,281              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 515,914 397,376 184,715              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 89,294                  
Short-duration insurance contract, cumulative number of reported claims | claim 54,000                  
Accident Year 2018 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 347,585 334,821 338,217              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 148,934 98,260 31,978              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 127,500                  
Short-duration insurance contract, cumulative number of reported claims | claim 11,000                  
Accident Year 2018 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 505,028 488,562 483,259              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 374,653 290,306 185,378              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 36,513                  
Short-duration insurance contract, cumulative number of reported claims | claim 45,000                  
Accident Year 2018 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 692,033 702,271 722,118              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 646,287 616,757 405,592              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 27,521                  
Short-duration insurance contract, cumulative number of reported claims | claim 43,000                  
Accident Year 2018 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 241,187 232,709 238,411              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 64,306 39,297 14,612              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 104,193                  
Accident Year 2018 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 76,242 77,482 78,929              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 12,728 10,884 6,241              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 29,909                  
Accident Year 2018 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 81,994 77,255 103,305              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 68,557 54,577 $ 23,078              
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 4,475                  
Accident Year 2019 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,214,463 1,341,042                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 225,344 72,302                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 749,747                  
Short-duration insurance contract, cumulative number of reported claims | claim 21,000                  
Accident Year 2019 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 716,430 725,245                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 380,454 172,478                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 156,496                  
Short-duration insurance contract, cumulative number of reported claims | claim 42,000                  
Accident Year 2019 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 377,674 396,508                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 81,026 28,357                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 243,075                  
Short-duration insurance contract, cumulative number of reported claims | claim 11,000                  
Accident Year 2019 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 428,769 523,746                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 228,366 142,822                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 82,221                  
Short-duration insurance contract, cumulative number of reported claims | claim 30,000                  
Accident Year 2019 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 905,441 901,702                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 785,227 460,749                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 56,083                  
Short-duration insurance contract, cumulative number of reported claims | claim 37,000                  
Accident Year 2019 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 295,992 302,420                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 49,871 20,803                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 192,023                  
Accident Year 2019 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 83,468 84,354                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 8,699 4,869                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 43,519                  
Accident Year 2019 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 118,039 114,807                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 65,718 $ 26,599                
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 6,928                  
Accident Year 2020 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,537,062                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 76,838                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 1,269,718                  
Short-duration insurance contract, cumulative number of reported claims | claim 17,000                  
Accident Year 2020 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 742,687                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 172,730                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 340,879                  
Short-duration insurance contract, cumulative number of reported claims | claim 42,000                  
Accident Year 2020 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 528,128                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 28,854                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 447,919                  
Short-duration insurance contract, cumulative number of reported claims | claim 10,000                  
Accident Year 2020 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 614,424                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 180,863                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 279,892                  
Short-duration insurance contract, cumulative number of reported claims | claim 34,000                  
Accident Year 2020 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 829,194                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 405,859                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 222,879                  
Short-duration insurance contract, cumulative number of reported claims | claim 31,000                  
Accident Year 2020 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 364,611                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 10,984                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 325,434                  
Accident Year 2020 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 98,109                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 4,586                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net 75,305                  
Accident Year 2020 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 134,134                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 15,243                  
Short-duration insurance contracts, incurred but not reported (IBNR) claims liability, net $ 86,160