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Reserve for Loss and Loss Expense (Claims Development) (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	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]
Net outstanding liabilities	$ 12,898,946
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	9,397,544
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,873,898
Reserve for loss and loss expense	4,580,903	$ 4,260,355
Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	372,496
Short-duration Insurance Contracts, Accident Year 2012 [Member]
Claims Development [Line Items]
Net outstanding liabilities	962,678	962,091	$ 968,536	$ 973,411	$ 973,644	$ 973,089	$ 998,028	$ 1,020,655	$ 1,071,290	$ 1,065,437
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 36,108
Short-duration Insurance Contract, Cumulative Number of Reported Claims	104,515
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 913,478	905,816	898,269	879,372	856,195	810,135	743,742	651,544	555,819	378,067
Short-duration Insurance Contracts, Accident Year 2013 [Member]
Claims Development [Line Items]
Net outstanding liabilities	957,958	973,739	984,858	987,763	1,002,316	1,021,007	1,047,230	1,062,045	1,044,142
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 40,736
Short-duration Insurance Contract, Cumulative Number of Reported Claims	91,756
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 911,657	904,825	891,841	872,331	833,823	748,758	644,475	518,872	335,956
Short-duration Insurance Contracts, Accident Year 2014[Member]
Claims Development [Line Items]
Net outstanding liabilities	1,094,367	1,089,529	1,100,208	1,104,218	1,124,014	1,146,990	1,133,798	1,107,513
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 48,550
Short-duration Insurance Contract, Cumulative Number of Reported Claims	95,610
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,020,961	1,002,157	981,868	936,425	855,959	736,154	614,075	405,898
Short-duration Insurance Contracts, Accident Year 2015 [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,103,592	1,108,860	1,119,441	1,138,313	1,144,830	1,130,513	1,114,081
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 56,165
Short-duration Insurance Contract, Cumulative Number of Reported Claims	94,874
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,000,509	967,857	929,222	845,868	725,385	581,203	376,641
Short-duration Insurance Contracts, Accident Year 2016 [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,171,273	1,180,829	1,199,734	1,227,142	1,203,634	1,188,608
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 90,598
Short-duration Insurance Contract, Cumulative Number of Reported Claims	95,559
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,025,264	983,852	892,390	764,331	617,958	387,272
Short-duration Insurance Contracts, Accident Year 2017 [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,268,941	1,288,526	1,313,585	1,313,372	1,270,110
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 122,313
Short-duration Insurance Contract, Cumulative Number of Reported Claims	99,424
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,050,258	954,792	829,134	678,453	433,440
Short-duration Insurance Contract, Accident Year 2018 [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,441,303	1,457,415	1,461,603	1,413,800
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 222,464
Short-duration Insurance Contract, Cumulative Number of Reported Claims	106,569
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,083,556	942,893	779,466	511,271
Short-Duration Insurance Contract, Accident Year 2019 [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,526,566	1,523,041	1,483,945
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 383,970
Short-duration Insurance Contract, Cumulative Number of Reported Claims	103,271
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 949,996	781,462	510,091
Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Net outstanding liabilities	1,587,607	1,591,972
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 562,065
Short-duration Insurance Contract, Cumulative Number of Reported Claims	93,515
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 831,976	572,302
Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Net outstanding liabilities	1,784,661
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 932,590
Short-duration Insurance Contract, Cumulative Number of Reported Claims	89,801
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 609,889
Standard Commercial Lines [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	2,812,608
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,399,252
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,515,789
Standard Commercial Lines [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,674,241
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,099,622
Liability for Unpaid Claims and Claims Adjustment Expense, Net	816,606
Standard Commercial Lines [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	3,107,304
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	2,393,027
Liability for Unpaid Claims and Claims Adjustment Expense, Net	717,704
Standard Commercial Lines [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	553,952
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	463,590
Liability for Unpaid Claims and Claims Adjustment Expense, Net	99,501
Standard Commercial Lines [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,579,137
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,481,032
Liability for Unpaid Claims and Claims Adjustment Expense, Net	98,204
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | General Liability [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	102,433
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	241,987
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,427
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	9,139
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	99
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	179,197	178,285	182,085	180,659	175,268	175,305	194,144	215,083	245,561	238,979
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 12,796
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,052
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 162,516	158,397	156,186	144,451	130,866	109,448	89,008	56,580	35,241	13,030
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	177,706	177,658	178,774	183,314	187,359	188,596	195,197	199,360	208,036	203,864
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 20,697
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,628,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 151,273	148,750	146,739	143,281	139,477	132,052	122,755	108,211	86,909	40,911
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	184,411	184,477	185,357	184,633	186,128	184,367	184,289	183,527	191,947	179,551
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 467
Short-duration Insurance Contract, Cumulative Number of Reported Claims	24,431,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 183,365	183,098	181,353	179,501	176,656	168,114	148,669	127,235	105,371	73,316
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	43,534	43,444	43,717	43,418	43,747	44,077	44,172	46,303	48,029	54,342
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 198
Short-duration Insurance Contract, Cumulative Number of Reported Claims	5,545,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 42,061	42,075	41,356	41,326	40,627	38,766	37,215	35,089	31,833	22,199
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	117,277	117,200	117,220	117,225	117,170	117,102	116,658	115,375	114,224	118,464
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,519,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 116,755	116,673	116,674	116,671	116,625	116,291	114,699	111,503	108,834	81,528
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	192,782	195,697	202,697	203,831	210,785	225,709	239,776	251,421	250,609
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 15,661
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,433
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 172,983	169,847	163,764	153,628	139,114	104,587	72,127	35,113	12,789
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	153,436	157,645	159,767	162,787	166,662	173,160	187,658	194,318	199,794
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 20,638
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,384,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 130,467	129,224	126,822	124,130	118,669	109,739	96,376	74,568	36,829
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	207,554	208,040	209,602	207,975	210,410	207,994	209,197	205,282	188,289
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 595
Short-duration Insurance Contract, Cumulative Number of Reported Claims	26,053,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 206,162	205,064	202,622	200,750	189,626	169,850	140,015	109,893	76,469
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	38,930	39,358	39,699	39,709	41,369	40,624	41,005	42,618	49,617
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 120
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,483,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 39,440	39,212	39,085	38,464	37,993	34,760	30,845	26,592	17,412
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	90,461	90,486	90,218	90,278	90,436	90,005	90,103	90,639	88,101
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3
Short-duration Insurance Contract, Cumulative Number of Reported Claims	5,715,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 90,891	90,917	90,646	90,696	90,840	90,350	90,446	87,874	60,244
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	230,247	229,679	237,125	234,082	239,333	257,132	249,946	244,312
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 21,413
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,677
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 198,772	187,352	179,192	154,957	121,969	79,972	46,825	14,901
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	161,021	159,604	160,646	164,420	172,515	182,579	187,065	199,346
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 21,285
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,495,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 130,726	127,858	124,077	119,392	113,626	100,876	78,944	35,924
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	214,992	216,461	217,334	218,172	219,925	216,824	212,725	200,534
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 875
Short-duration Insurance Contract, Cumulative Number of Reported Claims	28,079,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 213,689	212,481	209,655	202,821	180,701	148,884	117,169	80,810
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	57,483	57,302	58,093	58,517	59,806	62,548	60,949	55,962
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 746
Short-duration Insurance Contract, Cumulative Number of Reported Claims	4,067,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 55,729	55,708	55,458	52,940	49,460	44,911	40,584	28,914
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	136,151	136,237	136,212	138,155	138,751	136,820	136,249	141,192
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 10
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,517,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 136,141	135,928	136,008	137,418	137,883	136,634	132,909	101,131
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	211,768	214,176	219,204	233,249	246,990	245,710	254,720
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 25,873
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,532
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 173,697	157,071	144,216	116,804	78,668	39,978	14,665
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	170,577	172,572	176,242	179,642	183,604	194,639	193,729
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 20,748
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,554,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 129,019	124,046	120,097	112,601	98,195	77,320	33,857
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	262,054	261,386	260,565	259,495	253,074	240,958	220,994
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,826
Short-duration Insurance Contract, Cumulative Number of Reported Claims	29,837,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 255,600	249,905	238,142	211,515	175,866	132,260	91,347
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	52,200	52,325	54,454	55,925	57,245	53,768	52,871
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 801
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,967,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 50,005	49,839	49,073	46,571	42,710	36,014	24,189
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	112,937	112,582	112,496	111,566	111,750	109,513	110,270
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 12
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,407,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 112,410	112,117	110,969	110,994	109,829	106,182	79,048
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	246,643	252,733	263,245	277,986	272,048	277,214
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 41,647
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,763
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 181,770	164,136	133,757	89,431	46,549	15,684
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	155,210	156,540	166,009	176,248	184,946	196,774
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 24,850
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,585,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 119,800	115,159	109,166	98,037	78,531	34,525
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	291,674	290,359	285,304	285,302	274,367	255,187
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,226
Short-duration Insurance Contract, Cumulative Number of Reported Claims	31,754,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 277,242	264,858	233,939	200,701	155,720	106,022
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	53,147	53,367	53,835	54,993	53,792	52,335
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,010
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,851,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 50,536	48,786	45,308	39,973	36,848	24,655
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	123,005	123,567	124,487	125,937	126,185	121,927
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 23
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,743,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 122,909	123,601	123,828	122,930	118,789	83,966
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	278,607	289,883	301,384	293,128	293,747
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 67,475
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,219
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 167,002	131,980	92,355	49,470	17,366
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	154,159	162,672	175,853	184,306	195,202
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 25,096
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,809,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 116,426	110,645	100,645	82,216	40,375
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	326,461	322,197	324,291	329,389	301,274
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 10,110
Short-duration Insurance Contract, Cumulative Number of Reported Claims	33,066,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 296,600	262,349	220,422	178,823	117,287
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	43,606	48,067	51,524	48,698	46,624
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,642
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,892,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 39,940	40,359	36,950	31,337	21,865
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	154,119	153,664	149,044	149,106	138,773
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 54
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,904,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 153,750	152,018	148,589	142,338	99,047
Standard Commercial Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	332,013	345,224	336,326	317,934
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 126,438
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,641
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 155,538	108,421	60,784	19,531
Standard Commercial Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	173,428	181,151	193,818	193,894
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 34,218
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,129,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 119,904	105,903	84,780	41,122
Standard Commercial Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	350,310	345,547	352,487	347,908
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 23,671
Short-duration Insurance Contract, Cumulative Number of Reported Claims	35,714,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 291,725	243,713	193,788	134,867
Standard Commercial Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	60,393	62,427	57,202	55,024
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 7,655
Short-duration Insurance Contract, Cumulative Number of Reported Claims	4,256,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 48,144	44,316	39,791	29,995
Standard Commercial Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	194,016	192,558	190,834	183,177
Short-duration Insurance, Contracts Incurred But Not Reported (IBNR) Claims Liability, Net	$ 98
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,289,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 193,487	192,698	184,813	135,416
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	358,301	356,363	347,150
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 196,836
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,264
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 100,206	58,284	18,097
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	174,912	188,596	188,625
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 44,549
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,307,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 100,812	77,878	37,826
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	404,854	398,346	385,212
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 63,122
Short-duration Insurance Contract, Cumulative Number of Reported Claims	36,079,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 283,410	221,590	149,538
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	64,667	59,466	53,531
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 11,556
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,616,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 46,113	41,587	27,718
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	179,574	177,075	173,826
Short-duration Insurance, Contracts Incurred But Not Reported (IBNR) Claims Liability, Net	$ 530
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,300,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 177,825	172,768	130,891
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	360,302	361,554
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 252,458
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,076
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 58,699	21,858
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	168,594	168,643
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 61,878
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,495,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 68,277	29,559
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	381,163	381,654
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 121,558
Short-duration Insurance Contract, Cumulative Number of Reported Claims	30,095,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 198,034	139,016
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	73,680	71,836
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 11,225
Short-duration Insurance Contract, Cumulative Number of Reported Claims	5,364,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 57,210	43,376
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	225,278	232,060
Short-duration Insurance, Contracts Incurred But Not Reported (IBNR) Claims Liability, Net	$ 4,314
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,116,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 215,107	164,613
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	422,748
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 356,223
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,260
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 28,069
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	185,198
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 111,451
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,089,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 32,918
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	483,831
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 232,070
Short-duration Insurance Contract, Cumulative Number of Reported Claims	34,461,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 187,200
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	66,312
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 21,947
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,078,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 34,412
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	246,319
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 36,186
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,153,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 161,757
Standard Personal Lines | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,058,064
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	965,301
Liability for Unpaid Claims and Claims Adjustment Expense, Net	98,476
Standard Personal Lines | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	784,488
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	745,598
Liability for Unpaid Claims and Claims Adjustment Expense, Net	44,328
Standard Personal Lines | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,713
Standard Personal Lines | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | Homeowners [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,438
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	109,546	109,634	109,701	109,795	110,300	110,294	109,324	109,832	114,921	113,771
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,333,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 109,539	109,554	109,482	109,447	109,355	107,890	102,977	94,842	82,729	63,704
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	86,533	86,519	86,567	86,483	86,330	86,271	86,667	86,560	82,744	87,260
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 35
Short-duration Insurance Contract, Cumulative Number of Reported Claims	16,944,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 85,918	85,899	85,897	85,642	85,562	85,196	84,250	82,720	79,584	69,056
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	107,754	107,803	107,916	107,680	107,759	106,703	106,225	109,620	108,417
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 72
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,376,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 107,423	107,419	106,876	106,679	105,131	100,528	92,637	80,861	61,384
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	71,955	71,948	72,318	72,148	71,714	72,145	71,494	72,528	73,670
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 38
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,750,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 72,447	72,446	72,433	72,197	71,776	69,775	67,838	65,528	50,664
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2014[Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	107,566	107,106	107,104	106,821	107,452	106,757	109,325	102,250
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 79
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,509,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 107,108	106,478	105,709	104,055	99,173	92,589	83,739	62,519
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2014[Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	83,830	83,525	83,824	83,539	83,844	83,637	82,461	80,111
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 32
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,775,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 83,321	82,831	82,836	82,583	81,664	79,751	76,007	61,561
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	98,596	98,588	98,718	99,570	100,214	99,698	96,387
Short-duration Insurance, Contracts Incurred But Not Reported (IBNR) Claims Liability, Net	$ 109
Short-duration Insurance Contract, Cumulative Number of Reported Claims	20,865,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 97,761	97,275	95,997	92,102	87,163	76,470	58,725
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	74,682	74,673	74,978	74,723	76,559	76,400	76,637
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 478
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,750,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 74,096	74,052	74,079	72,927	72,202	70,078	52,589
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	99,858	99,544	101,140	100,202	98,032	92,727
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 357
Short-duration Insurance Contract, Cumulative Number of Reported Claims	19,826,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 98,977	98,080	94,372	86,752	76,823	57,961
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	60,855	61,735	61,723	62,391	60,931	60,105
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 465
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,895,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 60,449	61,187	60,082	59,546	57,333	42,252
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	103,557	103,260	103,653	105,139	101,880
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 447
Short-duration Insurance Contract, Cumulative Number of Reported Claims	20,744,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 100,521	97,628	91,479	82,730	62,854
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	68,938	70,064	70,365	67,978	59,167
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 570
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,386,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 68,078	67,767	67,193	63,290	45,466
Standard Personal Lines | Short-duration Insurance Contract, Accident Year 2018 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	112,418	112,030	113,569	111,594
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,100
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,682,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 107,026	99,982	89,628	69,721
Standard Personal Lines | Short-duration Insurance Contract, Accident Year 2018 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	68,931	69,832	68,526	62,961
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,289
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,607,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 66,634	65,348	64,137	49,430
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	115,993	115,688	114,043
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,649
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,845,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 102,930	92,162	69,699
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	73,816	72,772	64,306
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,027
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,001,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 69,911	67,631	49,680
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2020 | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	94,532	95,625
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 17,790
Short-duration Insurance Contract, Cumulative Number of Reported Claims	17,501,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 68,691	53,407
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2020 | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	112,523	109,033
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4,829
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,791,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 105,690	83,838
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2021 | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	108,244
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 28,461
Short-duration Insurance Contract, Cumulative Number of Reported Claims	18,931,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 65,325
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2021 | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	82,425
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 15,963
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,298,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 59,054
E&S Lines [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	922,755
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	495,422
Liability for Unpaid Claims and Claims Adjustment Expense, Net	430,176
E&S Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2012 [Member] | General Liability [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	2,843
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	44,083	44,348	44,622	46,444	45,988	46,165	46,149	43,175	42,621	42,367
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,911
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,064,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 41,299	40,615	39,832	38,298	36,278	32,343	25,064	16,430	7,914	$ 3,722
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	60,349	68,029	68,451	68,972	67,647	69,112	67,099	60,309	55,468
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,637
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,310,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 57,152	55,988	54,974	51,142	46,108	35,200	21,980	9,470	$ 2,715
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	74,270	70,846	71,153	71,206	71,719	69,929	63,505	55,316
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4,115
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,131,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 66,661	64,698	60,092	53,780	43,877	25,571	12,234	$ 2,353
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	87,662	90,126	90,355	90,488	82,404	76,432	75,498
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6,293
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,875,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 75,844	71,421	64,529	50,712	29,389	13,057	$ 3,036
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	102,476	104,730	105,120	104,655	96,416	94,451
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 19,208
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,968,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 75,004	69,448	56,581	33,950	16,195	$ 3,720
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	99,960	99,395	99,866	95,783	91,438
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16,217
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,797,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 68,266	53,238	34,179	14,672	$ 5,057
E&S Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	104,983	103,184	103,004	98,324
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 25,673
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,762,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 57,962	39,174	21,337	$ 5,509
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	117,736	118,298	117,087
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 56,323
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,553,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 35,844	17,812	$ 4,422
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	103,137	103,872
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 71,650
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,595,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 13,064	$ 3,695
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	128,099
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 111,132
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,223,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 4,326

X

- Definition

Undiscounted amount after reinsurance, of incurred-but-not-reported (IBNR) liabilities plus expected development on reported claims, for claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

+ References

No definition available.

+ Details

Name:	sigi_ShortDurationInsuranceContractsIncurredButNotReportedIbnrClaimsLiabilityNetSIGI
Namespace Prefix:	sigi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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The amount needed to reflect the estimated ultimate cost of settling claims relating to casualty insurance insured events that have occurred on or before a particular date (ordinarily, the balance sheet date) and the amount needed to provide for the estimated ultimate cost required to investigate and settle claims relating to insured events that have occurred on or before a particular date (ordinarily, the balance sheet date), whether or not reported to the insurer at that date.

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Amount, after reinsurance, of paid claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

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Undiscounted amount, after reinsurance, of incurred-but-not-reported (IBNR) liabilities plus expected development on reported claims, for claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

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Undiscounted amount, after reinsurance, of incurred claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

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Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense.

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Cumulative number of reported claims for short-duration insurance contracts.

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