XML 128 R96.htm IDEA: XBRL DOCUMENT v3.24.0.1

Reserve for Loss and Loss Expense (Claims Development) (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	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 ($)	Dec. 31, 2014 USD ($)
Claims Development [Line Items]
Net outstanding liabilities	$ 15,332,846
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	11,128,130
Liability for Unpaid Claims and Claims Adjustment Expense, Net	4,566,037
Reserve for loss and loss expense	5,336,911	$ 5,144,821
Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	361,321
Short-duration Insurance Contracts, Accident Year 2014[Member]
Claims Development [Line Items]
Net outstanding liabilities	1,087,700	1,090,345	$ 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	$ 33,872
Short-duration Insurance Contract, Cumulative Number of Reported Claims	95,785
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,040,893	1,032,400	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	1,105,039	1,103,543	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	$ 38,133
Short-duration Insurance Contract, Cumulative Number of Reported Claims	95,468
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,032,064	1,018,023	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	1,163,467	1,167,539	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	$ 47,702
Short-duration Insurance Contract, Cumulative Number of Reported Claims	96,324
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,088,453	1,061,952	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	1,287,882	1,273,039	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	$ 63,595
Short-duration Insurance Contract, Cumulative Number of Reported Claims	100,292
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,180,346	1,116,336	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	1,424,953	1,425,540	1,441,303	1,457,415	1,461,603	1,413,800
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 98,900
Short-duration Insurance Contract, Cumulative Number of Reported Claims	107,541
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,252,623	1,187,744	1,083,556	942,893	779,466	511,271
Short-Duration Insurance Contract, Accident Year 2019 [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,523,313	1,529,859	1,526,566	1,523,041	1,483,945
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 169,855
Short-duration Insurance Contract, Cumulative Number of Reported Claims	104,668
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,247,100	1,109,628	949,996	781,462	510,091
Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Net outstanding liabilities	1,531,446	1,550,195	1,587,607	1,591,972
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 243,526
Short-duration Insurance Contract, Cumulative Number of Reported Claims	95,537
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,152,227	988,463	831,976	572,302
Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Net outstanding liabilities	1,774,984	1,781,054	1,784,661
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 438,488
Short-duration Insurance Contract, Cumulative Number of Reported Claims	99,553
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,134,930	934,965	609,889
Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Net outstanding liabilities	2,096,742	2,073,343
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 690,322
Short-duration Insurance Contract, Cumulative Number of Reported Claims	105,549
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 1,155,527	699,789
Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Net outstanding liabilities	2,337,320
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,169,504
Short-duration Insurance Contract, Cumulative Number of Reported Claims	101,414
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 843,967
Standard Commercial Lines [Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	3,468,736
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,712,824
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,874,944
Standard Commercial Lines [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,671,146
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,112,122
Liability for Unpaid Claims and Claims Adjustment Expense, Net	767,784
Standard Commercial Lines [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	3,956,413
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	3,021,770
Liability for Unpaid Claims and Claims Adjustment Expense, Net	939,644
Standard Commercial Lines [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	640,270
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	547,925
Liability for Unpaid Claims and Claims Adjustment Expense, Net	101,601
Standard Commercial Lines [Member] | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	2,008,483
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,875,394
Liability for Unpaid Claims and Claims Adjustment Expense, Net	133,412
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | General Liability [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	119,032
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Workers Compensation [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	208,760
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Commercial Automobile [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,001
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Business Owners' Policies [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	9,256
Standard Commercial Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Commercial Property [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	323
Standard Commercial Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	226,407	228,933	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	$ 13,296
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,725
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 208,521	204,212	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	156,750	158,479	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	$ 15,581
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,495
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 134,338	132,809	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	215,073	214,816	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	$ 276
Short-duration Insurance Contract, Cumulative Number of Reported Claims	28,447
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 214,564	213,847	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	57,649	57,355	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	$ (21)
Short-duration Insurance Contract, Cumulative Number of Reported Claims	4,067
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 57,670	56,861	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	136,370	136,112	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	$ 8
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,517
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 136,362	136,107	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	213,653	210,137	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	$ 16,595
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,596
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 186,336	179,117	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	166,042	169,008	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	$ 15,698
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,554
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 133,272	132,235	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	263,115	262,766	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	$ 470
Short-duration Insurance Contract, Cumulative Number of Reported Claims	30,332
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 260,328	257,668	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	51,457	52,514	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	$ 24
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,971
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 51,308	51,120	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	112,974	112,915	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	$ 8
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,407
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 112,568	112,391	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	244,782	243,669	246,643	252,733	263,245	277,986	272,048	277,214
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 22,161
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,900
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 211,725	199,032	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	147,732	151,961	155,210	156,540	166,009	176,248	184,946	196,774
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 17,164
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,587
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 123,232	122,186	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	294,878	294,297	291,674	290,359	285,304	285,302	274,367	255,187
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,457
Short-duration Insurance Contract, Cumulative Number of Reported Claims	32,324
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 288,512	284,870	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	52,930	53,201	53,147	53,367	53,835	54,993	53,792	52,335
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 280
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,857
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 52,427	52,070	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	123,067	123,126	123,005	123,567	124,487	125,937	126,185	121,927
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,743
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 123,203	123,265	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	293,448	283,379	278,607	289,883	301,384	293,128	293,747
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 33,861
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,426
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 241,879	201,948	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	148,949	151,221	154,159	162,672	175,853	184,306	195,202
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16,019
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,814
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 123,573	120,468	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	326,832	325,654	326,461	322,197	324,291	329,389	301,274
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,984
Short-duration Insurance Contract, Cumulative Number of Reported Claims	33,627
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 318,047	309,810	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	42,408	42,374	43,606	48,067	51,524	48,698	46,624
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 416
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,897
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 41,217	40,845	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	155,408	154,942	154,119	153,664	149,044	149,106	138,773
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 22
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,907
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 155,236	154,689	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	329,102	324,567	332,013	345,224	336,326	317,934
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 57,847
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,924
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 236,812	197,286	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	163,884	167,974	173,428	181,151	193,818	193,894
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 20,739
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,136
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 129,869	126,206	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	346,213	348,202	350,310	345,547	352,487	347,908
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,190
Short-duration Insurance Contract, Cumulative Number of Reported Claims	36,286
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 330,584	319,819	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	55,586	56,625	60,393	62,427	57,202	55,024
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,169
Short-duration Insurance Contract, Cumulative Number of Reported Claims	4,264
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 52,496	51,239	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	196,527	196,413	194,016	192,558	190,834	183,177
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 40
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,294
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 196,605	196,376	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	362,139	366,184	358,301	356,363	347,150
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 98,841
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,767
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 213,020	160,680	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	159,225	164,940	174,912	188,596	188,625
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 22,629
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,330
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 119,875	112,649	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	410,432	407,051	404,854	398,346	385,212
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16,701
Short-duration Insurance Contract, Cumulative Number of Reported Claims	36,653
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 376,550	331,152	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	64,721	65,762	64,667	59,466	53,531
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,129
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,650
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 60,076	52,887	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	180,832	180,605	179,574	177,075	173,826
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 88
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,315
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 180,179	179,538	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	361,163	352,834	360,302	361,554
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 142,886
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,050
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 159,209	100,356	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	143,384	159,229	168,594	168,643
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 21,785
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,551
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 102,142	87,211	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	374,293	375,636	381,163	381,654
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 37,371
Short-duration Insurance Contract, Cumulative Number of Reported Claims	30,533
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 306,355	254,365	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	73,320	73,077	73,680	71,836
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,777
Short-duration Insurance Contract, Cumulative Number of Reported Claims	5,443
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 66,478	60,596	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	226,915	226,107	225,278	232,060
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,345
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,155
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 223,902	220,953	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	414,204	414,279	422,748
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 209,078
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,916
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 131,157	71,664	28,069
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	173,784	185,151	185,198
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 52,182
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,580
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 96,674	76,015	32,918
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	510,825	512,673	483,831
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 92,709
Short-duration Insurance Contract, Cumulative Number of Reported Claims	37,184
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 352,383	283,411	187,200
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	72,231	63,648	66,312
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 11,352
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,520
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 54,651	47,436	34,412
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	237,831	239,822	246,319
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 859
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,983
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 235,217	227,259	161,757
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2022 | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	482,279	482,590
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 308,245
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,275
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 93,422	31,502
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2022 | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	207,156	207,206
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 70,491
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,963
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 99,894	45,814
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2022 | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	581,223	572,421
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 170,627
Short-duration Insurance Contract, Cumulative Number of Reported Claims	39,879
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 336,516	216,180
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2022 | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	89,025	86,194
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16,496
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,750
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 66,581	36,421
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2022 | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	296,974	297,318
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4,467
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,828
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 285,250	186,677
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2023 | General Liability [Member]
Claims Development [Line Items]
Net outstanding liabilities	541,559
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 453,175
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,213
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 30,743
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2023 | Workers Compensation [Member]
Claims Development [Line Items]
Net outstanding liabilities	204,240
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 106,226
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,331
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 49,253
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2023 | Commercial Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	633,529
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 308,059
Short-duration Insurance Contract, Cumulative Number of Reported Claims	36,860
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 237,931
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2023 | Business Owners' Policies [Member]
Claims Development [Line Items]
Net outstanding liabilities	80,943
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 23,721
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,129
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 45,021
Standard Commercial Lines [Member] | Short-Duration Insurance Contract, Accident Year 2023 | Commercial Property [Member]
Claims Development [Line Items]
Net outstanding liabilities	341,585
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 53,704
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,129
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 226,872
Standard Personal Lines | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,144,541
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,025,143
Liability for Unpaid Claims and Claims Adjustment Expense, Net	125,940
Standard Personal Lines | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	863,067
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	809,870
Liability for Unpaid Claims and Claims Adjustment Expense, Net	58,334
Standard Personal Lines | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Personal Automobile [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	6,542
Standard Personal Lines | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Homeowners [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,137
Standard Personal Lines | Short-duration Insurance Contracts, Accident Year 2014[Member] | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	107,390	107,543	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	$ 8
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,510
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 107,381	107,325	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	83,796	83,819	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	$ 37
Short-duration Insurance Contract, Cumulative Number of Reported Claims	8,776
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 83,782	83,782	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	98,939	98,669	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	$ 53
Short-duration Insurance Contract, Cumulative Number of Reported Claims	20,866
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 98,483	97,920	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	74,265	74,237	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	$ 44
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,754
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 74,108	74,108	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	100,458	100,395	99,858	99,544	101,140	100,202	98,032	92,727
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 113
Short-duration Insurance Contract, Cumulative Number of Reported Claims	19,827
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 100,315	99,656	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	60,453	60,841	60,855	61,735	61,723	62,391	60,931	60,105
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 45
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,896
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 60,480	60,474	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	105,243	105,079	103,557	103,260	103,653	105,139	101,880
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 435
Short-duration Insurance Contract, Cumulative Number of Reported Claims	20,751
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 104,114	103,556	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	68,919	68,902	68,938	70,064	70,365	67,978	59,167
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 463
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,391
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 68,454	68,282	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	113,037	113,647	112,418	112,030	113,569	111,594
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 781
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,685
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 110,894	109,644	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	68,581	68,416	68,931	69,832	68,526	62,961
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 757
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,609
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 67,726	67,739	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	119,632	118,669	115,993	115,688	114,043
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,871
Short-duration Insurance Contract, Cumulative Number of Reported Claims	22,872
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 115,919	109,844	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	72,856	73,070	73,816	72,772	64,306
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,061
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,010
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 71,603	70,880	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	89,027	90,179	94,532	95,625
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2,537
Short-duration Insurance Contract, Cumulative Number of Reported Claims	17,548
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 83,137	76,710	68,691	53,407
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2020 | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	112,590	113,804	112,523	109,033
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1,345
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,835
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 110,578	109,145	105,690	83,838
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2021 | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	105,088	102,777	108,244
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,963
Short-duration Insurance Contract, Cumulative Number of Reported Claims	19,730
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 94,480	84,743	65,325
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2021 | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	84,189	83,295	82,425
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3,612
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,919
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 79,399	77,018	59,054
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2022 | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	133,623	121,030
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16,991
Short-duration Insurance Contract, Cumulative Number of Reported Claims	21,262
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 107,778	75,994
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2022 | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	100,389	93,826
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5,017
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,869
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 91,788	68,832
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2023 | Personal Automobile [Member]
Claims Development [Line Items]
Net outstanding liabilities	172,104
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 45,030
Short-duration Insurance Contract, Cumulative Number of Reported Claims	25,893
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 102,642
Standard Personal Lines | Short-Duration Insurance Contract, Accident Year 2023 | Homeowners [Member]
Claims Development [Line Items]
Net outstanding liabilities	137,029
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 24,058
Short-duration Insurance Contract, Cumulative Number of Reported Claims	7,051
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 101,952
E&S Lines [Member] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	1,110,366
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	598,439
Liability for Unpaid Claims and Claims Adjustment Expense, Net	517,988
E&S Lines [Member] | Short-Duration Insurance Contracts, Accident Years Prior to 2014 [Member] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	6,061
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2014[Member] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	75,436	74,538	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	$ 4,631
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,888,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 69,498	68,648	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] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	91,424	90,263	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	$ 5,159
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,899,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 83,587	81,396	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] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	101,105	101,873	102,476	104,730	105,120	104,655	96,416	94,451
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6,299
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,015,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 90,665	81,932	75,004	69,448	56,581	33,950	16,195	$ 3,720
E&S Lines [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	106,663	102,045	99,960	99,395	99,866	95,783	91,438
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 9,143
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,866,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 88,294	77,090	68,266	53,238	34,179	14,672	$ 5,057
E&S Lines [Member] | Short-duration Insurance Contract, Accident Year 2018 [Member] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	106,490	105,756	104,983	103,184	103,004	98,324
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 12,001
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,843,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 82,549	73,605	57,962	39,174	21,337	$ 5,509
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	114,802	117,113	117,736	118,298	117,087
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 23,476
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,752,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 73,779	57,701	35,844	17,812	$ 4,422
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	91,077	95,832	103,137	103,872
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 30,090
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,891,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 46,349	27,861	13,064	$ 3,695
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2021 | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	120,191	125,436	128,099
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 60,356
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,991,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 37,213	15,835	$ 4,326
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2022 | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	145,918	146,999
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 96,255
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,944,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 21,618	$ 4,198
E&S Lines [Member] | Short-Duration Insurance Contract, Accident Year 2023 | Casualty Insurance Product Line [Member]
Claims Development [Line Items]
Net outstanding liabilities	157,260
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 137,488
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,242,000
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 4,887

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

Name:	us-gaap_ClaimsDevelopmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-3

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (cc)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-3

+ Details

Name:	us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpensePropertyCasualtyLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (b)
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4B

+ Details

Name:	us-gaap_ShortdurationInsuranceContractsCumulativePaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (a)
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4D

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4E
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4E

+ Details

Name:	us-gaap_ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsLiabilityNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (a)
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4B

+ Details

Name:	us-gaap_ShortdurationInsuranceContractsIncurredClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4C
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4C

+ Details

Name:	us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (b)
-SubTopic 40
-Topic 944
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480081/944-40-50-4D

+ Details

Name:	us-gaap_ShortdurationInsuranceContractsNumberOfReportedClaims
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=sigi_ShortDurationInsuranceContractsAccidentYearsPriorTo2014Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2014Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractsAccidentYear2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractsAccidentYear2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	sigi_LineOfBusinessBySegmentAxis=sigi_StandardCommercialLinesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_GeneralLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_WorkersCompensationInsuranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=sigi_CommercialAutomobileMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=sigi_BusinessOwnersPoliciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=sigi_CommercialPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	sigi_LineOfBusinessBySegmentAxis=sigi_StandardPersonalLinesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=sigi_PersonalAutomobileMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=sigi_HomeownersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	sigi_LineOfBusinessBySegmentAxis=sigi_ESLinesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=sigi_CasualtyInsuranceProductLineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: