Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Schedule of Incurred Claims Development) (Details) $ in Millions	Dec. 31, 2022 USD ($) Claim	Dec. 31, 2021 USD ($)	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 ($)	Dec. 31, 2013 USD ($)
Commercial Multiple Peril Line [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	$ 4,275.8
Cumulative Paid Losses and ALAE, Net of Reinsurance	2,940.5
Unallocated loss adjustment expense	20.8
Net reserves	1,423.9
Commercial Multiple Peril Line [Member] | Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	408.3	$ 410.1	$ 414.0	$ 419.0	$ 421.9	$ 418.6	$ 412.9	$ 398.1
IBNR	$ 10.6
Cumulative Incurred Claim Count | Claim	14,497
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 384.6	379.6	372.7	358.5	329.6	289.6	241.0	152.9
Commercial Multiple Peril Line [Member] | Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	397.2	396.7	400.1	400.0	401.0	402.5	398.2
IBNR	$ 8.3
Cumulative Incurred Claim Count | Claim	14,428
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 365.4	347.7	331.8	306.8	261.9	215.2	128.7
Commercial Multiple Peril Line [Member] | Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	493.6	494.0	491.5	487.5	481.1	473.9
IBNR	$ 17.4
Cumulative Incurred Claim Count | Claim	15,359
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 435.6	414.5	377.6	328.8	264.1	157.2
Commercial Multiple Peril Line [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	495.8	490.6	489.5	495.6	511.1
IBNR	$ 24.2
Cumulative Incurred Claim Count | Claim	15,864
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 403.6	362.9	326.4	274.1	165.7
Commercial Multiple Peril Line [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	542.6	533.1	527.0	520.2
IBNR	$ 44.8
Cumulative Incurred Claim Count | Claim	14,948
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 396.3	348.7	288.5	156.5
Commercial Multiple Peril Line [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	531.5	546.7	562.1
IBNR	$ 84.1
Cumulative Incurred Claim Count | Claim	13,066
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 364.2	318.6	200.8
Commercial Multiple Peril Line [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	658.7	673.5
IBNR	$ 130.9
Cumulative Incurred Claim Count | Claim	14,753
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 392.6	245.1
Commercial Multiple Peril Line [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	748.1
IBNR	$ 351.1
Cumulative Incurred Claim Count | Claim	12,094
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 198.2
Commercial Multiple Peril Line [Member] | Years 2015 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	1,335.3
Commercial Multiple Peril Line [Member] | Years 2014 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	67.8
Workers' Compensation Line [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	1,437.1
Cumulative Paid Losses and ALAE, Net of Reinsurance	947.6
Unallocated loss adjustment expense	18.8
Net reserves	593.9
Workers' Compensation Line [Member] | Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	116.2	118.9	119.4	121.1	121.4	121.0	120.1	126.0	$ 134.0	$ 133.0
IBNR	$ 6.1
Cumulative Incurred Claim Count | Claim	9,178
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 104.5	104.0	102.6	101.2	98.2	94.8	87.9	78.9	58.0	24.0
Workers' Compensation Line [Member] | Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	112.9	116.4	118.2	120.7	123.1	124.3	125.8	138.0	143.5
IBNR	$ 7.5
Cumulative Incurred Claim Count | Claim	8,807
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 98.5	97.6	96.2	93.7	89.8	85.0	75.3	58.5	25.7
Workers' Compensation Line [Member] | Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	113.8	116.3	119.0	122.2	125.8	132.1	136.0	157.0
IBNR	$ 10.5
Cumulative Incurred Claim Count | Claim	8,911
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 93.2	91.2	89.1	86.2	81.8	72.2	55.0	24.2
Workers' Compensation Line [Member] | Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	122.3	124.9	128.3	133.5	139.9	152.8	158.9
IBNR	$ 10.0
Cumulative Incurred Claim Count | Claim	12,811
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 102.1	100.1	97.2	93.3	84.4	67.0	29.2
Workers' Compensation Line [Member] | Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	129.6	132.4	136.7	139.9	148.7	159.6
IBNR	$ 11.0
Cumulative Incurred Claim Count | Claim	13,415
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 102.6	99.0	92.7	82.0	63.7	28.5
Workers' Compensation Line [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	149.2	150.8	152.6	161.3	165.2
IBNR	$ 14.4
Cumulative Incurred Claim Count | Claim	14,905
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 112.0	104.2	91.7	72.0	32.2
Workers' Compensation Line [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	163.2	162.9	165.0	170.5
IBNR	$ 16.7
Cumulative Incurred Claim Count | Claim	15,307
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 116.2	102.4	75.7	30.4
Workers' Compensation Line [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	150.6	166.8	167.1
IBNR	$ 24.2
Cumulative Incurred Claim Count | Claim	11,904
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 91.8	71.4	28.8
Workers' Compensation Line [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	180.8	178.5
IBNR	$ 30.9
Cumulative Incurred Claim Count | Claim	14,040
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 85.3	40.6
Workers' Compensation Line [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	198.5
IBNR	$ 64.6
Cumulative Incurred Claim Count | Claim	14,269
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 41.4
Workers' Compensation Line [Member] | Years 2013 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	489.5
Workers' Compensation Line [Member] | Years 2012 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	85.6
Commercial Automobile Line [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	1,144.2
Cumulative Paid Losses and ALAE, Net of Reinsurance	717.6
Unallocated loss adjustment expense	4.9
Net reserves	447.9
Commercial Automobile Line [Member] | Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	$ 163.3	160.8	159.5	161.6	151.4	144.9	144.5
Cumulative Incurred Claim Count | Claim	10,944
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 152.0	143.8	137.0	125.1	92.0	56.5	26.1
Commercial Automobile Line [Member] | Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	176.0	175.6	169.4	164.3	155.6	146.3
IBNR	$ 1.8
Cumulative Incurred Claim Count | Claim	10,910
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 160.9	144.4	125.8	95.5	64.8	24.9
Commercial Automobile Line [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	176.1	171.5	162.9	157.6	170.1
IBNR	$ 6.0
Cumulative Incurred Claim Count | Claim	10,613
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 142.7	114.5	83.2	52.7	26.8
Commercial Automobile Line [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	174.6	169.7	167.9	161.0
IBNR	$ 15.1
Cumulative Incurred Claim Count | Claim	9,787
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 126.5	94.8	64.5	27.1
Commercial Automobile Line [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	140.2	141.5	153.2
IBNR	$ 34.0
Cumulative Incurred Claim Count | Claim	5,895
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 71.4	42.1	21.0
Commercial Automobile Line [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	156.5	154.1
IBNR	$ 63.0
Cumulative Incurred Claim Count | Claim	6,066
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 45.2	17.7
Commercial Automobile Line [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	157.5
IBNR	$ 100.1
Cumulative Incurred Claim Count | Claim	5,374
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 18.9
Commercial Automobile Line [Member] | Years 2016 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	426.6
Commercial Automobile Line [Member] | Years 2015 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	16.4
Core - General Liability And Umbrella - Occurrence [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	572.5
Cumulative Paid Losses and ALAE, Net of Reinsurance	290.9
Unallocated loss adjustment expense	3.4
Net reserves	296.9
Core - General Liability And Umbrella - Occurrence [Member] | Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	38.6	39.0	39.6	40.1	42.5	46.9	50.4	41.5	44.4	52.1
IBNR	$ 1.9
Cumulative Incurred Claim Count | Claim	1,458
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 35.3	35.3	34.9	34.1	32.7	28.6	21.7	12.7	5.3	$ 1.1
Core - General Liability And Umbrella - Occurrence [Member] | Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	54.0	54.0	53.4	54.0	53.8	60.8	57.9	48.9	70.7
IBNR	$ 3.5
Cumulative Incurred Claim Count | Claim	1,442
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 48.4	47.4	46.0	45.5	38.2	30.3	17.2	7.9	$ 1.6
Core - General Liability And Umbrella - Occurrence [Member] | Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	45.5	49.1	50.5	52.1	53.8	58.6	57.9	66.6
IBNR	$ 3.2
Cumulative Incurred Claim Count | Claim	1,303
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 40.7	38.3	37.3	32.6	25.5	14.1	7.5	$ 1.4
Core - General Liability And Umbrella - Occurrence [Member] | Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	54.2	54.5	53.7	55.8	57.8	61.0	58.5
IBNR	$ 5.5
Cumulative Incurred Claim Count | Claim	1,199
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 38.7	34.4	31.7	25.3	14.8	7.3	0.7
Core - General Liability And Umbrella - Occurrence [Member] | Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	61.0	62.9	63.0	66.3	67.1	58.2
IBNR	$ 8.4
Cumulative Incurred Claim Count | Claim	1,027
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 42.6	33.9	27.1	19.3	9.0	2.3
Core - General Liability And Umbrella - Occurrence [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	63.2	63.3	60.3	61.1	58.8
IBNR	$ 13.5
Cumulative Incurred Claim Count | Claim	952
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 38.1	27.2	18.8	4.4	1.0
Core - General Liability And Umbrella - Occurrence [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	69.3	60.3	60.0	58.9
IBNR	$ 15.8
Cumulative Incurred Claim Count | Claim	827
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 28.2	16.5	8.7	4.3
Core - General Liability And Umbrella - Occurrence [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	53.4	58.9	56.2
IBNR	$ 29.1
Cumulative Incurred Claim Count | Claim	518
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 11.9	9.2	2.1
Core - General Liability And Umbrella - Occurrence [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	70.0	58.3
IBNR	$ 41.0
Cumulative Incurred Claim Count | Claim	473
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 6.6	1.5
Core - General Liability And Umbrella - Occurrence [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	63.3
IBNR	$ 50.5
Cumulative Incurred Claim Count | Claim	395
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 0.4
Core - General Liability And Umbrella - Occurrence [Member] | Years 2013 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	281.6
Core - General Liability And Umbrella - Occurrence [Member] | Years 2012 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	11.9
Specialty Property And Casualty [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	1,383.3
Cumulative Paid Losses and ALAE, Net of Reinsurance	904.2
Unallocated loss adjustment expense	23.5
Net reserves	541.8
Specialty Property And Casualty [Member] | Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	158.9	157.3	156.6	154.1	153.4	152.4	157.9
IBNR	$ 5.4
Cumulative Incurred Claim Count | Claim	6,473
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 143.7	134.4	126.9	117.1	95.3	75.1	40.5
Specialty Property And Casualty [Member] | Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	199.1	195.6	193.9	190.1	185.3	189.6
IBNR	$ 10.1
Cumulative Incurred Claim Count | Claim	6,862
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 168.5	155.6	138.7	125.9	102.6	55.5
Specialty Property And Casualty [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	191.1	190.2	193.7	194.1	193.0
IBNR	$ 13.6
Cumulative Incurred Claim Count | Claim	6,440
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 158.6	140.3	124.9	107.9	56.0
Specialty Property And Casualty [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	237.1	225.7	209.4	212.2
IBNR	$ 24.0
Cumulative Incurred Claim Count | Claim	6,496
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 164.9	136.5	113.9	71.5
Specialty Property And Casualty [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	164.9	170.8	181.1
IBNR	$ 35.1
Cumulative Incurred Claim Count | Claim	5,232
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 101.2	84.0	40.4
Specialty Property And Casualty [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	213.9	202.9
IBNR	$ 63.0
Cumulative Incurred Claim Count | Claim	5,897
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 106.6	59.2
Specialty Property And Casualty [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	218.3
IBNR	$ 110.3
Cumulative Incurred Claim Count | Claim	5,175
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 60.7
Specialty Property And Casualty [Member] | Years 2016 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	479.1
Specialty Property And Casualty [Member] | Years 2015 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	39.2
Specialty General Liability Claims Made [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	870.6
Cumulative Paid Losses and ALAE, Net of Reinsurance	519.6
Unallocated loss adjustment expense	6.1
Net reserves	362.4
Specialty General Liability Claims Made [Member] | Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	97.4	94.0	94.0	88.4	95.1	98.6	99.5
IBNR	$ 1.5
Cumulative Incurred Claim Count | Claim	974
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 92.0	85.2	79.3	74.3	65.3	42.4	$ 10.8
Specialty General Liability Claims Made [Member] | Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	93.6	92.5	94.1	96.1	100.6	99.1
IBNR	$ 1.6
Cumulative Incurred Claim Count | Claim	1,067
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 86.3	81.0	74.8	65.5	40.9	$ 12.1
Specialty General Liability Claims Made [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	121.6	121.7	121.2	117.8	112.2
IBNR	$ 5.8
Cumulative Incurred Claim Count | Claim	1,176
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 102.9	93.6	78.9	50.3	14.4
Specialty General Liability Claims Made [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	127.6	125.6	119.5	119.8
IBNR	$ 12.9
Cumulative Incurred Claim Count | Claim	1,258
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 95.4	77.0	53.3	16.5
Specialty General Liability Claims Made [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	123.3	134.2	137.3
IBNR	$ 22.3
Cumulative Incurred Claim Count | Claim	1,379
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 75.0	50.6	16.8
Specialty General Liability Claims Made [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	144.8	148.2
IBNR	$ 54.7
Cumulative Incurred Claim Count | Claim	1,372
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 49.9	15.8
Specialty General Liability Claims Made [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	162.3
IBNR	$ 99.0
Cumulative Incurred Claim Count | Claim	2,108
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 18.1
Specialty General Liability Claims Made [Member] | Years 2016 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	351.0
Specialty General Liability Claims Made [Member] | Years 2015 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	5.3
Personal Automobile Lines [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	2,014.0
Cumulative Paid Losses and ALAE, Net of Reinsurance	1,342.8
Unallocated loss adjustment expense	17.6
Net reserves	746.1
Personal Automobile Lines [Member] | Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	409.3	406.7	400.3	395.3	394.2
IBNR	$ 6.5
Cumulative Incurred Claim Count | Claim	43,092
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 382.8	353.1	307.4	237.2	$ 121.7
Personal Automobile Lines [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	438.9	436.1	431.8	431.2
IBNR	$ 14.5
Cumulative Incurred Claim Count | Claim	42,402
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 385.1	336.6	262.2	131.0
Personal Automobile Lines [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	312.3	347.0	378.0
IBNR	$ 34.4
Cumulative Incurred Claim Count | Claim	26,334
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 231.8	179.2	95.9
Personal Automobile Lines [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	411.6	407.2
IBNR	$ 84.3
Cumulative Incurred Claim Count | Claim	30,164
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 225.9	106.4
Personal Automobile Lines [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	441.9
IBNR	$ 195.1
Cumulative Incurred Claim Count | Claim	29,366
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 117.2
Personal Automobile Lines [Member] | Years 2018 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	671.2
Personal Automobile Lines [Member] | Years 2017 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	57.3
Homeowners [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	1,804.0
Cumulative Paid Losses and ALAE, Net of Reinsurance	1,510.5
Unallocated loss adjustment expense	4.1
Net reserves	309.5
Homeowners [Member] | Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	340.7	342.1	345.3	344.5
IBNR	$ 2.9
Cumulative Incurred Claim Count | Claim	33,747
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 329.2	322.5	311.7	$ 234.7
Homeowners [Member] | Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	424.9	423.3	418.8
IBNR	$ 4.3
Cumulative Incurred Claim Count | Claim	35,294
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 408.1	387.7	$ 281.5
Homeowners [Member] | Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	489.9	461.4
IBNR	$ 18.9
Cumulative Incurred Claim Count | Claim	38,925
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 449.1	$ 306.9
Homeowners [Member] | Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and ALAE, Net of Reinsurance	548.5
IBNR	$ 141.5
Cumulative Incurred Claim Count | Claim	29,556
Cumulative Paid Losses and ALAE, Net of Reinsurance	$ 324.1
Homeowners [Member] | Years 2019 to 2022 [Member]
Claims Development [Line Items]
Total reserves for accident years	293.5
Homeowners [Member] | Years 2018 and Prior [Member]
Claims Development [Line Items]
Total reserves for accident years	$ 11.9