Liability for Losses and Loss Expenses, Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Details) Claim in Thousands, $ in Thousands	Dec. 31, 2021 USD ($) Claim	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Personal Automobile [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 1,428,518
Personal Automobile [Member] | 2012 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	136,542	$ 136,648	$ 136,677	$ 136,141	$ 136,463	$ 136,552	$ 136,493	$ 135,592	$ 133,201	$ 130,415
Total IBNR plus expected development on reported claims	$ 98
Cumulative number of reported claims | Claim	69
Personal Automobile [Member] | 2013 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 132,787	132,690	132,853	132,934	132,604	132,643	131,594	130,737	124,965
Total IBNR plus expected development on reported claims	$ 106
Cumulative number of reported claims | Claim	66
Personal Automobile [Member] | 2014 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 126,977	126,861	126,734	126,779	126,200	124,210	124,806	124,426
Total IBNR plus expected development on reported claims	$ 131
Cumulative number of reported claims | Claim	71
Personal Automobile [Member] | 2015 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 142,010	142,073	142,408	142,493	139,181	139,333	137,569
Total IBNR plus expected development on reported claims	$ 293
Cumulative number of reported claims | Claim	70
Personal Automobile [Member] | 2016 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 156,436	156,935	157,943	157,516	153,937	150,216
Total IBNR plus expected development on reported claims	$ 728
Cumulative number of reported claims | Claim	73
Personal Automobile [Member] | 2017 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 173,730	174,784	175,939	127,728	166,690
Total IBNR plus expected development on reported claims	$ 1,328
Cumulative number of reported claims | Claim	79
Personal Automobile [Member] | 2018 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 180,787	181,558	183,358	186,580
Total IBNR plus expected development on reported claims	$ 3,069
Cumulative number of reported claims | Claim	81
Personal Automobile [Member] | 2019 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 156,300	157,689	161,056
Total IBNR plus expected development on reported claims	$ 5,151
Cumulative number of reported claims | Claim	68
Personal Automobile [Member] | 2020 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 103,585	111,483
Total IBNR plus expected development on reported claims	$ 7,372
Cumulative number of reported claims | Claim	43
Personal Automobile [Member] | 2021 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 119,364
Total IBNR plus expected development on reported claims	$ 20,654
Cumulative number of reported claims | Claim	45
Homeowners [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 654,692
Homeowners [Member] | 2012 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	54,556	54,548	54,537	54,523	54,381	54,281	54,351	54,468	54,794	53,962
Total IBNR plus expected development on reported claims	$ 0
Cumulative number of reported claims | Claim	18
Homeowners [Member] | 2013 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 51,053	51,064	51,008	50,971	50,988	50,874	51,122	51,121	50,887
Total IBNR plus expected development on reported claims	$ 0
Cumulative number of reported claims | Claim	13
Homeowners [Member] | 2014 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 57,371	57,367	57,402	57,288	57,332	57,680	58,378	56,916
Total IBNR plus expected development on reported claims	$ 0
Cumulative number of reported claims | Claim	16
Homeowners [Member] | 2015 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 63,043	62,993	63,099	63,071	63,053	63,925	63,359
Total IBNR plus expected development on reported claims	$ 19
Cumulative number of reported claims | Claim	13
Homeowners [Member] | 2016 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 63,409	63,279	63,355	63,735	64,064	62,443
Total IBNR plus expected development on reported claims	$ 12
Cumulative number of reported claims | Claim	12
Homeowners [Member] | 2017 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 79,065	79,247	79,305	79,911	79,283
Total IBNR plus expected development on reported claims	$ 144
Cumulative number of reported claims | Claim	17
Homeowners [Member] | 2018 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 82,566	82,905	83,385	81,965
Total IBNR plus expected development on reported claims	$ 538
Cumulative number of reported claims | Claim	18
Homeowners [Member] | 2019 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 73,234	73,554	73,294
Total IBNR plus expected development on reported claims	$ 912
Cumulative number of reported claims | Claim	16
Homeowners [Member] | 2020 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 62,718	61,633
Total IBNR plus expected development on reported claims	$ 1,567
Cumulative number of reported claims | Claim	13
Homeowners [Member] | 2021 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 67,677
Total IBNR plus expected development on reported claims	$ 6,208
Cumulative number of reported claims | Claim	11
Commercial Automobile [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 673,489
Commercial Automobile [Member] | 2012 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	31,922	31,930	31,896	31,803	31,648	31,278	31,435	30,606	27,720	26,557
Total IBNR plus expected development on reported claims	$ 15
Cumulative number of reported claims | Claim	8
Commercial Automobile [Member] | 2013 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 36,165	36,181	36,569	36,435	36,404	35,240	34,751	33,749	32,902
Total IBNR plus expected development on reported claims	$ 53
Cumulative number of reported claims | Claim	8
Commercial Automobile [Member] | 2014 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 49,291	49,308	49,168	49,284	48,213	47,326	44,544	42,760
Total IBNR plus expected development on reported claims	$ 91
Cumulative number of reported claims | Claim	11
Commercial Automobile [Member] | 2015 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 53,793	54,619	54,517	54,259	51,412	48,323	46,526
Total IBNR plus expected development on reported claims	$ 234
Cumulative number of reported claims | Claim	12
Commercial Automobile [Member] | 2016 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 66,085	66,894	67,127	65,905	57,353	54,302
Total IBNR plus expected development on reported claims	$ 338
Cumulative number of reported claims | Claim	13
Commercial Automobile [Member] | 2017 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 65,310	67,249	67,697	67,927	61,484
Total IBNR plus expected development on reported claims	$ 895
Cumulative number of reported claims | Claim	13
Commercial Automobile [Member] | 2018 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 83,043	82,313	81,396	79,307
Total IBNR plus expected development on reported claims	$ 2,306
Cumulative number of reported claims | Claim	15
Commercial Automobile [Member] | 2019 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 90,290	91,245	88,864
Total IBNR plus expected development on reported claims	$ 7,365
Cumulative number of reported claims | Claim	16
Commercial Automobile [Member] | 2020 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 87,766	90,367
Total IBNR plus expected development on reported claims	$ 14,996
Cumulative number of reported claims | Claim	14
Commercial Automobile [Member] | 2021 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 109,824
Total IBNR plus expected development on reported claims	$ 41,282
Cumulative number of reported claims | Claim	14
Commercial Multi-Peril [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 617,599
Commercial Multi-Peril [Member] | 2012 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	36,844	36,662	36,876	36,525	36,214	35,755	34,117	32,449	30,716	29,789
Total IBNR plus expected development on reported claims	$ 0
Cumulative number of reported claims | Claim	6
Commercial Multi-Peril [Member] | 2013 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 37,630	37,495	37,453	37,365	37,981	37,205	37,292	35,679	35,683
Total IBNR plus expected development on reported claims	$ 0
Cumulative number of reported claims | Claim	6
Commercial Multi-Peril [Member] | 2014 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 52,933	52,926	53,116	53,294	52,336	51,843	50,135	48,204
Total IBNR plus expected development on reported claims	$ 79
Cumulative number of reported claims | Claim	7
Commercial Multi-Peril [Member] | 2015 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 45,420	45,366	45,873	45,104	44,728	43,874	42,070
Total IBNR plus expected development on reported claims	$ 135
Cumulative number of reported claims | Claim	6
Commercial Multi-Peril [Member] | 2016 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 48,823	48,732	48,871	48,267	46,988	43,005
Total IBNR plus expected development on reported claims	$ 373
Cumulative number of reported claims | Claim	6
Commercial Multi-Peril [Member] | 2017 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 55,076	54,812	56,517	56,043	56,185
Total IBNR plus expected development on reported claims	$ 674
Cumulative number of reported claims | Claim	7
Commercial Multi-Peril [Member] | 2018 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 67,810	67,749	66,470	66,265
Total IBNR plus expected development on reported claims	$ 3,653
Cumulative number of reported claims | Claim	7
Commercial Multi-Peril [Member] | 2019 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 76,326	73,836	71,865
Total IBNR plus expected development on reported claims	$ 8,159
Cumulative number of reported claims | Claim	7
Commercial Multi-Peril [Member] | 2020 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 79,910	83,195
Total IBNR plus expected development on reported claims	$ 15,880
Cumulative number of reported claims | Claim	8
Commercial Multi-Peril [Member] | 2021 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 116,827
Total IBNR plus expected development on reported claims	$ 37,194
Cumulative number of reported claims | Claim	6
Workers Compensation [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 491,969
Workers Compensation [Member] | 2012 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	36,056	36,014	35,932	35,954	36,468	37,163	37,926	38,827	39,516	$ 39,142
Total IBNR plus expected development on reported claims	$ 39
Cumulative number of reported claims | Claim	5
Workers Compensation [Member] | 2013 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 42,427	42,341	42,651	42,555	42,327	42,828	44,289	47,027	$ 46,325
Total IBNR plus expected development on reported claims	$ 70
Cumulative number of reported claims | Claim	6
Workers Compensation [Member] | 2014 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 47,620	47,849	47,693	47,540	48,537	49,288	51,553	$ 51,508
Total IBNR plus expected development on reported claims	$ 68
Cumulative number of reported claims | Claim	6
Workers Compensation [Member] | 2015 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 42,225	42,597	43,006	44,986	45,991	49,615	$ 53,332
Total IBNR plus expected development on reported claims	$ 328
Cumulative number of reported claims | Claim	5
Workers Compensation [Member] | 2016 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 43,559	44,098	44,969	47,883	49,802	$ 58,814
Total IBNR plus expected development on reported claims	$ 532
Cumulative number of reported claims | Claim	5
Workers Compensation [Member] | 2017 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 49,557	51,464	52,687	56,351	$ 60,450
Total IBNR plus expected development on reported claims	$ 1,461
Cumulative number of reported claims | Claim	5
Workers Compensation [Member] | 2018 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 47,912	52,514	55,291	$ 62,197
Total IBNR plus expected development on reported claims	$ 2,171
Cumulative number of reported claims | Claim	6
Workers Compensation [Member] | 2019 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 57,728	59,624	$ 60,998
Total IBNR plus expected development on reported claims	$ 3,474
Cumulative number of reported claims | Claim	6
Workers Compensation [Member] | 2020 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 57,850	$ 57,172
Total IBNR plus expected development on reported claims	$ 5,494
Cumulative number of reported claims | Claim	5
Workers Compensation [Member] | 2021 [Member]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net [Abstract]
Incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 67,035
Total IBNR plus expected development on reported claims	$ 21,111
Cumulative number of reported claims | Claim	6