XML 78 R84.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
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, 2019
USD ($)
claim
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Dec. 31, 2012
USD ($)
Dec. 31, 2011
USD ($)
Dec. 31, 2010
USD ($)
Claims Development [Line Items]                    
Reserves for loss and loss adjustment expenses, net of reinsurance $ 11,227,535                  
Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 9,080,745                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 5,188,434                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 106,200                  
Reserves for loss and loss adjustment expenses, net of reinsurance 3,998,511                  
Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 6,034,851                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 4,357,720                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 193,837                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,870,968                  
Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 2,843,002                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 1,823,850                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 15,104                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,034,256                  
Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 4,070,528                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 3,376,880                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 4,313                  
Reserves for loss and loss adjustment expenses, net of reinsurance 697,961                  
Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 6,218,646                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 5,709,499                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 1,019                  
Reserves for loss and loss adjustment expenses, net of reinsurance 510,166                  
Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 2,759,034                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 1,586,176                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 383,199                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,556,057                  
Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 640,355                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 125,236                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 765,323                  
Reserves for loss and loss adjustment expenses, net of reinsurance 1,280,442                  
Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,153,343                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 967,462                  
Reserves for loss and loss adjustment expenses before 2010, net of reinsurance 798                  
Reserves for loss and loss adjustment expenses, net of reinsurance 186,679                  
Accident Year 2010 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 561,579 $ 564,873 $ 569,440 $ 571,637 $ 572,785 $ 575,528 $ 588,602 $ 589,921 $ 616,023 $ 612,467
Cumulative paid claims and claim adjustment expenses, net of reinsurance 531,085 522,939 506,283 489,077 459,478 414,945 334,054 246,647 128,948 45,194
IBNR $ 19,742                  
Cumulative Number of Reported Claims | claim 22,000                  
Accident Year 2010 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 424,195 424,374 427,698 429,762 429,952 426,622 420,604 411,527 355,305 352,138
Cumulative paid claims and claim adjustment expenses, net of reinsurance 392,672 388,405 382,665 374,013 362,078 344,631 320,154 281,280 215,882 108,675
IBNR $ 13,552                  
Cumulative Number of Reported Claims | claim 45,000                  
Accident Year 2010 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 182,860 182,717 177,757 174,796 172,493 176,653 177,951 179,344 165,689 147,632
Cumulative paid claims and claim adjustment expenses, net of reinsurance 179,865 178,756 171,206 164,894 160,466 144,336 129,619 108,438 58,851 14,806
IBNR $ 62                  
Cumulative Number of Reported Claims | claim 4,000                  
Accident Year 2010 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 329,768 329,976 330,297 330,586 331,615 332,748 328,901 330,224 320,098 310,591
Cumulative paid claims and claim adjustment expenses, net of reinsurance 328,006 327,863 327,240 326,804 324,997 313,262 295,355 263,639 208,790 136,029
IBNR $ 144                  
Cumulative Number of Reported Claims | claim 37,000                  
Accident Year 2010 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 345,546 345,777 346,074 346,493 346,380 345,937 355,602 358,254 370,080 385,319
Cumulative paid claims and claim adjustment expenses, net of reinsurance 344,989 344,908 344,887 343,899 342,773 340,066 346,622 337,688 325,163 245,037
IBNR $ 233                  
Cumulative Number of Reported Claims | claim 19,000                  
Accident Year 2010 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 249,472 249,599 250,596 252,900 256,271 265,455 276,049 288,146 298,265 290,438
Cumulative paid claims and claim adjustment expenses, net of reinsurance 198,822 191,532 181,857 166,361 150,665 128,476 105,912 76,845 45,338 17,814
IBNR 14,322                  
Accident Year 2010 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 99,944 95,374 94,986 100,065 104,732 102,424 118,712 120,272 123,497 135,639
Cumulative paid claims and claim adjustment expenses, net of reinsurance 28,431 22,355 18,821 14,261 11,699 11,260 8,701 5,571 4,003 2,867
IBNR 15,731                  
Accident Year 2010 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 50,362 50,630 50,398 50,571 50,694 51,230 51,186 52,306 55,399 58,367
Cumulative paid claims and claim adjustment expenses, net of reinsurance 49,690 49,749 49,001 48,745 46,141 44,550 43,634 42,153 37,483 $ 23,424
IBNR 208                  
Accident Year 2011 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 642,774 632,382 643,195 647,091 651,973 656,976 657,679 671,537 665,420  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 591,990 573,236 554,152 522,369 469,004 377,769 265,071 141,192 48,830  
IBNR $ 22,746                  
Cumulative Number of Reported Claims | claim 23,000                  
Accident Year 2011 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 473,766 471,471 475,729 474,076 472,087 470,026 457,134 444,887 413,429  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 436,905 428,811 420,945 408,304 385,759 355,909 309,509 236,207 106,899  
IBNR $ 17,276                  
Cumulative Number of Reported Claims | claim 46,000                  
Accident Year 2011 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 176,230 175,689 176,606 173,309 176,936 189,988 187,074 165,291 179,818  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 170,205 168,526 166,949 158,678 150,487 134,253 102,898 62,305 18,726  
IBNR $ 2,187                  
Cumulative Number of Reported Claims | claim 4,000                  
Accident Year 2011 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 343,433 343,566 342,094 341,200 341,394 331,732 328,320 320,920 312,224  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 340,799 340,360 338,325 333,987 321,814 296,370 262,685 211,756 135,350  
IBNR $ 964                  
Cumulative Number of Reported Claims | claim 37,000                  
Accident Year 2011 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 451,064 451,410 449,529 450,325 457,182 460,030 463,253 471,678 478,520  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 450,439 450,352 447,538 446,944 445,234 440,937 436,718 417,730 303,016  
IBNR $ 649                  
Cumulative Number of Reported Claims | claim 21,000                  
Accident Year 2011 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 299,130 292,762 296,280 304,780 307,969 299,244 304,352 309,836 290,770  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 232,452 220,566 208,347 192,724 169,219 133,808 97,476 52,231 17,812  
IBNR 16,563                  
Accident Year 2011 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 72,091 74,109 78,246 83,850 85,299 89,031 98,051 93,993 88,650  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 23,686 21,463 20,164 18,638 15,684 14,042 6,395 4,848 2,593  
IBNR 14,075                  
Accident Year 2011 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 84,432 84,651 84,246 84,522 84,791 86,326 84,914 87,837 95,201  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 83,250 83,169 82,094 81,560 78,357 75,778 73,142 58,702 $ 31,402  
IBNR 490                  
Accident Year 2012 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 714,020 715,996 721,460 711,287 707,326 701,144 700,539 691,803    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 651,000 620,507 578,617 511,601 415,890 298,095 157,316 57,568    
IBNR $ 32,727                  
Cumulative Number of Reported Claims | claim 23,000                  
Accident Year 2012 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 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 459,119 451,991 437,196 419,588 387,368 339,560 255,063 115,536    
IBNR $ 24,736                  
Cumulative Number of Reported Claims | claim 48,000                  
Accident Year 2012 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 245,338 244,730 245,945 239,458 251,230 265,690 242,541 238,978    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 232,160 223,988 214,821 190,584 159,285 128,245 86,734 21,697    
IBNR $ 7,091                  
Cumulative Number of Reported Claims | claim 5,000                  
Accident Year 2012 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 365,806 366,541 364,328 364,084 355,609 342,588 326,831 314,309    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 361,755 360,681 355,631 344,326 312,342 273,446 215,214 136,844    
IBNR $ 807                  
Cumulative Number of Reported Claims | claim 37,000                  
Accident Year 2012 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 507,416 508,354 506,464 507,509 533,491 538,141 537,716 529,564    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 504,342 503,614 499,355 498,207 515,520 504,954 454,731 281,830    
IBNR $ 2,229                  
Cumulative Number of Reported Claims | claim 28,000                  
Accident Year 2012 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 331,270 334,588 336,492 333,982 325,224 330,882 335,867 331,991    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 257,010 241,318 219,637 187,196 152,590 111,538 62,037 22,329    
IBNR 17,481                  
Accident Year 2012 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 67,205 69,361 67,878 72,441 73,653 73,670 73,230 72,366    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 20,004 17,982 15,738 13,234 11,167 10,815 6,097 1,127    
IBNR 11,249                  
Accident Year 2012 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 84,555 84,746 83,822 83,814 85,334 86,330 94,661 103,833    
Cumulative paid claims and claim adjustment expenses, net of reinsurance 82,541 81,673 78,971 77,412 70,524 64,098 51,641 $ 15,663    
IBNR 1,032                  
Accident Year 2013 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 803,856 809,250 802,908 782,039 782,260 790,314 750,054      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 693,306 647,891 587,102 471,648 330,928 188,240 63,293      
IBNR $ 49,079                  
Cumulative Number of Reported Claims | claim 25,000                  
Accident Year 2013 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 541,926 542,274 547,000 543,238 546,995 547,295 552,570      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 479,104 466,580 447,894 414,160 363,028 277,538 117,900      
IBNR $ 29,205                  
Cumulative Number of Reported Claims | claim 53,000                  
Accident Year 2013 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 285,262 280,018 271,469 249,797 243,887 248,080 269,993      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 258,394 249,005 207,020 177,525 119,567 63,951 23,939      
IBNR $ 14,062                  
Cumulative Number of Reported Claims | claim 6,000                  
Accident Year 2013 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 365,953 366,822 367,264 376,860 368,894 349,136 327,514      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 362,152 353,424 343,556 322,441 267,253 218,596 142,929      
IBNR $ 1,592                  
Cumulative Number of Reported Claims | claim 39,000                  
Accident Year 2013 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 546,766 548,673 552,192 553,680 577,353 586,382 576,784      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 540,158 539,553 538,304 531,474 536,630 488,140 314,122      
IBNR $ 3,405                  
Cumulative Number of Reported Claims | claim 30,000                  
Accident Year 2013 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 303,568 299,224 293,686 285,032 275,539 270,382 319,491      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 226,083 205,716 178,174 144,405 110,306 63,718 28,910      
IBNR 25,073                  
Accident Year 2013 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 31,752 35,120 38,551 42,419 46,025 50,355 63,995      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 5,349 4,418 3,396 3,008 2,158 1,897 647      
IBNR 12,626                  
Accident Year 2013 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 109,699 111,895 112,579 111,945 114,123 112,684 141,563      
Cumulative paid claims and claim adjustment expenses, net of reinsurance 107,606 106,045 104,326 101,539 92,619 74,573 $ 36,578      
IBNR 643                  
Accident Year 2014 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 870,017 863,899 851,044 846,644 848,641 847,034        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 680,436 594,488 480,418 338,365 190,876 78,921        
IBNR $ 83,500                  
Cumulative Number of Reported Claims | claim 26,000                  
Accident Year 2014 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 604,029 615,435 617,242 627,767 637,307 639,436        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 521,141 503,915 471,235 412,611 319,743 148,405        
IBNR $ 44,633                  
Cumulative Number of Reported Claims | claim 57,000                  
Accident Year 2014 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 258,781 239,982 244,454 260,498 247,373 253,992        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 216,228 199,337 176,134 138,678 83,694 19,446        
IBNR $ 26,194                  
Cumulative Number of Reported Claims | claim 6,000                  
Accident Year 2014 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 413,424 413,589 416,123 418,161 385,251 363,913        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 402,013 394,063 365,376 328,125 237,665 155,572        
IBNR $ 4,385                  
Cumulative Number of Reported Claims | claim 42,000                  
Accident Year 2014 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 664,416 664,169 663,342 664,718 712,320 707,121        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 655,332 648,072 632,796 613,530 599,119 372,670        
IBNR $ 4,366                  
Cumulative Number of Reported Claims | claim 34,000                  
Accident Year 2014 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 324,941 325,497 331,339 319,573 320,226 320,579        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 227,684 198,196 155,207 115,873 68,992 21,280        
IBNR 34,043                  
Accident Year 2014 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 42,541 41,671 45,758 49,478 57,558 63,561        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 7,595 5,808 4,175 3,354 1,729 377        
IBNR 15,347                  
Accident Year 2014 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 98,912 99,250 100,011 97,279 96,636 113,126        
Cumulative paid claims and claim adjustment expenses, net of reinsurance 93,160 91,452 88,317 82,172 66,869 $ 38,803        
IBNR 1,685                  
Accident Year 2015 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 966,662 964,598 961,441 986,655 951,028          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 676,037 538,071 382,185 210,773 82,712          
IBNR $ 134,615                  
Cumulative Number of Reported Claims | claim 25,000                  
Accident Year 2015 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 626,431 641,169 650,997 690,525 712,800          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 512,933 477,541 421,734 323,744 139,320          
IBNR $ 60,862                  
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 $ 292,401 276,842 275,608 258,780 260,216          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 216,575 187,664 139,835 85,470 20,415          
IBNR $ 37,634                  
Cumulative Number of Reported Claims | claim 7,000                  
Accident Year 2015 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 432,415 431,376 423,180 417,053 389,660          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 397,666 370,037 324,976 265,083 160,024          
IBNR $ 7,808                  
Cumulative Number of Reported Claims | claim 46,000                  
Accident Year 2015 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 718,506 726,748 728,186 731,950 743,454          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 699,770 690,037 668,012 612,369 395,440          
IBNR $ 10,676                  
Cumulative Number of Reported Claims | claim 37,000                  
Accident Year 2015 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 293,718 252,959 230,856 232,272 259,922          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 178,657 141,348 91,198 48,445 17,866          
IBNR 43,622                  
Accident Year 2015 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 39,682 45,115 50,099 57,897 69,977          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 4,416 4,099 3,272 2,481 2,069          
IBNR 19,040                  
Accident Year 2015 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 129,492 130,391 131,755 117,563 127,259          
Cumulative paid claims and claim adjustment expenses, net of reinsurance 122,621 118,603 109,090 89,153 $ 53,477          
IBNR 2,478                  
Accident Year 2016 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,031,150 1,019,893 1,010,984 1,018,009            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 558,539 390,231 208,991 69,477            
IBNR $ 245,835                  
Cumulative Number of Reported Claims | claim 25,000                  
Accident Year 2016 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 660,508 684,700 696,339 702,716            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 504,850 446,072 338,835 142,998            
IBNR $ 71,710                  
Cumulative Number of Reported Claims | claim 57,000                  
Accident Year 2016 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 402,929 361,996 325,241 311,099            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 255,841 201,854 102,661 28,631            
IBNR $ 56,934                  
Cumulative Number of Reported Claims | claim 8,000                  
Accident Year 2016 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 443,268 442,210 430,911 431,261            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 390,359 341,423 279,381 184,516            
IBNR $ 18,162                  
Cumulative Number of Reported Claims | claim 45,000                  
Accident Year 2016 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 758,881 764,278 777,270 773,945            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 728,122 712,815 671,219 417,424            
IBNR $ 12,383                  
Cumulative Number of Reported Claims | claim 40,000                  
Accident Year 2016 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 268,508 246,019 253,501 241,533            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 140,411 100,262 61,787 19,895            
IBNR 51,973                  
Accident Year 2016 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 64,957 71,404 70,281 72,657            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 5,928 5,573 4,783 2,498            
IBNR 23,676                  
Accident Year 2016 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 181,002 181,757 174,570 168,129            
Cumulative paid claims and claim adjustment expenses, net of reinsurance 168,605 157,491 133,576 $ 78,936            
IBNR 4,891                  
Accident Year 2017 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,122,209 1,100,127 1,066,362              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 453,389 255,849 80,037              
IBNR $ 377,307                  
Cumulative Number of Reported Claims | claim 25,000                  
Accident Year 2017 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 689,559 733,505 762,093              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 468,817 362,299 153,456              
IBNR $ 107,981                  
Cumulative Number of Reported Claims | claim 57,000                  
Accident Year 2017 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 339,021 332,864 333,758              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 163,003 96,456 36,579              
IBNR $ 112,457                  
Cumulative Number of Reported Claims | claim 9,000                  
Accident Year 2017 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 430,499 428,708 430,768              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 327,135 267,587 180,755              
IBNR $ 31,607                  
Cumulative Number of Reported Claims | claim 41,000                  
Accident Year 2017 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 748,451 753,803 753,512              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 718,949 690,029 445,560              
IBNR $ 18,189                  
Cumulative Number of Reported Claims | claim 46,000                  
Accident Year 2017 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 239,788 221,769 232,010              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 69,465 40,138 16,473              
IBNR 85,671                  
Accident Year 2017 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 70,749 80,508 76,701              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 15,356 12,810 6,282              
IBNR 29,999                  
Accident Year 2017 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 199,497 200,510 206,672              
Cumulative paid claims and claim adjustment expenses, net of reinsurance 171,745 141,389 $ 72,132              
IBNR 11,224                  
Accident Year 2018 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,131,202 1,104,631                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 264,392 86,858                
IBNR $ 606,500                  
Cumulative Number of Reported Claims | claim 23,000                  
Accident Year 2018 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 724,463 778,964                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 397,464 171,006                
IBNR $ 153,587                  
Cumulative Number of Reported Claims | claim 55,000                  
Accident Year 2018 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 322,952 335,728                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 99,789 28,231                
IBNR $ 168,475                  
Cumulative Number of Reported Claims | claim 9,000                  
Accident Year 2018 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 462,756 442,788                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 281,651 180,162                
IBNR $ 67,700                  
Cumulative Number of Reported Claims | claim 40,000                  
Accident Year 2018 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 750,780 760,474                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 662,185 415,206                
IBNR $ 33,738                  
Cumulative Number of Reported Claims | claim 52,000                  
Accident Year 2018 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 211,227 222,100                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 41,018 11,092                
IBNR 109,087                  
Accident Year 2018 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 72,505 77,820                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 8,230 6,141                
IBNR 36,930                  
Accident Year 2018 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 112,152 108,342                
Cumulative paid claims and claim adjustment expenses, net of reinsurance 65,193 $ 34,004                
IBNR 19,159                  
Accident Year 2019 | Other liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 1,237,276                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 88,260                  
IBNR $ 937,110                  
Cumulative Number of Reported Claims | claim 20,000                  
Accident Year 2019 | Workers' compensation                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 783,244                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 184,715                  
IBNR $ 372,381                  
Cumulative Number of Reported Claims | claim 50,000                  
Accident Year 2019 | Professional liability                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 337,228                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 31,790                  
IBNR $ 259,157                  
Cumulative Number of Reported Claims | claim 9,000                  
Accident Year 2019 | Commercial automobile                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 483,206                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 185,344                  
IBNR $ 162,432                  
Cumulative Number of Reported Claims | claim 37,000                  
Accident Year 2019 | Short-tail lines                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 726,820                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 405,213                  
IBNR $ 168,528                  
Cumulative Number of Reported Claims | claim 42,000                  
Accident Year 2019 | Casualty                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance $ 237,412                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 14,574                  
IBNR 196,623                  
Accident Year 2019 | Monoline excess                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 78,929                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 6,241                  
IBNR 48,526                  
Accident Year 2019 | Property                    
Claims Development [Line Items]                    
Loss and loss expenses incurred, net of reinsurance 103,240                  
Cumulative paid claims and claim adjustment expenses, net of reinsurance 23,051                  
IBNR $ 52,334