Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance (Detail) $ in Millions	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,678.3
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	2,052.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	1,175.0
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	35.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	913.0
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	185.8	$ 187.8	$ 189.0	$ 192.8	$ 193.5	$ 200.0	$ 205.8	$ 206.0	$ 202.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	177.5	174.4	170.0	162.4	146.6	122.9	91.0	53.8	17.6
IBNR & Expected Development on Reported Claims	$ 3.9
Cumulative Number of Reported Claims | claim	8,490
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 181.0	182.3	182.1	184.4	183.6	189.7	196.0	189.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	170.3	163.4	157.5	142.4	120.8	89.1	52.8	17.2
IBNR & Expected Development on Reported Claims	$ 5.8
Cumulative Number of Reported Claims | claim	7,453
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 214.3	216.0	220.4	227.2	224.3	222.6	217.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	192.2	179.6	163.7	135.2	100.4	60.2	17.6
IBNR & Expected Development on Reported Claims	$ 11.4
Cumulative Number of Reported Claims | claim	7,397
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 210.0	212.3	211.9	213.2	215.2	213.0
Cumulative Paid Losses & ALAE, Net of Reinsurance	172.8	154.5	131.6	95.9	52.2	15.0
IBNR & Expected Development on Reported Claims	$ 19.0
Cumulative Number of Reported Claims | claim	6,684
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 224.8	226.4	228.6	237.1	232.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	162.8	131.5	91.4	51.9	16.5
IBNR & Expected Development on Reported Claims	$ 32.5
Cumulative Number of Reported Claims | claim	6,306
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 248.3	243.1	250.6	246.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	149.5	95.5	52.8	17.4
IBNR & Expected Development on Reported Claims	$ 59.7
Cumulative Number of Reported Claims | claim	6,038
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 249.0	244.3	253.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	88.0	38.7	11.5
IBNR & Expected Development on Reported Claims	$ 92.5
Cumulative Number of Reported Claims | claim	6,251
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 269.5	278.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	47.0	15.0
IBNR & Expected Development on Reported Claims	$ 163.8
Cumulative Number of Reported Claims | claim	5,852
U.S. Operations [Member] | Excess and Surplus Lines [Member] | Liability [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 269.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	14.9
IBNR & Expected Development on Reported Claims	$ 207.5
Cumulative Number of Reported Claims | claim	4,199
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 1,193.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	768.7
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	42.3
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	467.5
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	151.6	154.0	153.7	154.0	158.2	157.5	159.0	155.1	140.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	144.0	143.1	139.8	135.1	126.1	111.3	85.9	57.5	23.2
IBNR & Expected Development on Reported Claims	$ 4.4
Cumulative Number of Reported Claims | claim	28,181
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 146.2	146.7	147.7	151.5	153.3	149.7	146.3	140.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	135.0	131.9	127.9	120.8	105.8	80.7	51.0	20.1
IBNR & Expected Development on Reported Claims	$ 5.1
Cumulative Number of Reported Claims | claim	23,657
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 128.9	130.6	131.1	133.2	136.7	133.2	126.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	114.7	109.7	102.8	93.6	74.0	49.4	18.9
IBNR & Expected Development on Reported Claims	$ 7.0
Cumulative Number of Reported Claims | claim	18,975
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 111.9	111.5	114.5	116.9	121.9	115.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	93.5	86.1	75.3	58.7	38.8	17.4
IBNR & Expected Development on Reported Claims	$ 10.1
Cumulative Number of Reported Claims | claim	16,346
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 103.1	102.3	101.7	106.7	107.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	73.6	64.2	48.8	35.0	17.2
IBNR & Expected Development on Reported Claims	$ 14.2
Cumulative Number of Reported Claims | claim	14,622
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 104.7	99.3	99.9	96.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	67.6	48.6	31.7	11.1
IBNR & Expected Development on Reported Claims	$ 15.1
Cumulative Number of Reported Claims | claim	11,802
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 135.3	129.5	121.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	70.9	44.4	16.3
IBNR & Expected Development on Reported Claims	$ 37.2
Cumulative Number of Reported Claims | claim	13,473
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 160.9	147.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	51.9	19.4
IBNR & Expected Development on Reported Claims	$ 54.6
Cumulative Number of Reported Claims | claim	15,267
U.S. Operations [Member] | Specialty Admitted [Member] | Liability [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 151.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	17.5
IBNR & Expected Development on Reported Claims	$ 89.4
Cumulative Number of Reported Claims | claim	12,867
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 430.0
Cumulative Paid Losses & ALAE, Net of Reinsurance	214.8
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	1.7
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	216.9
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	25.8	26.0	26.6	26.9	28.2	32.5	35.0	35.0	0.0
Cumulative Paid Losses & ALAE, Net of Reinsurance	25.7	25.7	25.7	25.4	24.0	22.0	17.8	11.8	0.0
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative Number of Reported Claims | claim	820
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 24.6	24.9	24.5	24.0	25.8	28.6	28.3	27.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	24.2	23.5	22.6	21.4	19.9	16.9	8.6	2.3
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	641
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 18.3	19.5	19.8	19.0	21.1	21.5	20.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	17.9	17.5	17.6	14.2	10.9	6.3	1.9
IBNR & Expected Development on Reported Claims	$ 0.3
Cumulative Number of Reported Claims | claim	622
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 35.4	36.2	33.7	26.0	22.4	22.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	32.3	25.5	24.1	15.1	5.4	2.3
IBNR & Expected Development on Reported Claims	$ 0.6
Cumulative Number of Reported Claims | claim	1,044
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 37.1	34.0	33.2	29.5	29.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	26.2	20.8	15.6	8.3	1.8
IBNR & Expected Development on Reported Claims	$ 1.4
Cumulative Number of Reported Claims | claim	1,840
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 42.9	45.1	44.8	44.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	28.9	24.6	11.9	2.4
IBNR & Expected Development on Reported Claims	$ 7.8
Cumulative Number of Reported Claims | claim	3,238
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 78.3	61.8	60.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	38.0	24.9	3.5
IBNR & Expected Development on Reported Claims	$ 7.0
Cumulative Number of Reported Claims | claim	3,724
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 73.2	70.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	16.7	4.5
IBNR & Expected Development on Reported Claims	$ 39.7
Cumulative Number of Reported Claims | claim	4,224
U.S. Operations [Member] | Specialty Admitted [Member] | Professional [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 94.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	4.9
IBNR & Expected Development on Reported Claims	$ 75.3
Cumulative Number of Reported Claims | claim	4,432
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 66.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	14.0
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	0.6
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	52.7
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	1.7	1.7	2.0	2.6	3.6	3.4	3.4	3.9	0.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.7	1.7	1.7	1.7	1.2	1.3	1.4	1.6	0.0
IBNR & Expected Development on Reported Claims	$ 0.0
Cumulative Number of Reported Claims | claim	80
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 3.6	3.5	3.9	4.0	4.3	4.9	6.7	7.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	3.4	3.3	3.4	3.3	3.3	3.3	3.3	3.6
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	129
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 0.9	0.9	1.7	2.5	4.6	8.6	10.0
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.9	0.9	0.9	0.9	0.9	0.9	0.4
IBNR & Expected Development on Reported Claims	$ 0.0
Cumulative Number of Reported Claims | claim	50
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 4.7	4.8	6.0	8.9	13.1	13.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	4.1	4.1	4.0	4.0	3.3	1.1
IBNR & Expected Development on Reported Claims	$ 0.6
Cumulative Number of Reported Claims | claim	50
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 1.2	5.5	9.5	14.3	14.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.3	0.3	0.2	0.1	0.2
IBNR & Expected Development on Reported Claims	$ 0.9
Cumulative Number of Reported Claims | claim	24
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 6.2	11.2	15.0	15.0
Cumulative Paid Losses & ALAE, Net of Reinsurance	2.2	2.2	1.6	1.3
IBNR & Expected Development on Reported Claims	$ 1.0
Cumulative Number of Reported Claims | claim	57
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 7.6	16.2	16.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.0	0.1	0.3
IBNR & Expected Development on Reported Claims	$ 7.6
Cumulative Number of Reported Claims | claim	96
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 17.4	20.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.7
IBNR & Expected Development on Reported Claims	$ 15.3
Cumulative Number of Reported Claims | claim	114
U.S. Operations [Member] | Specialty Admitted [Member] | Specialty [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 22.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.7
IBNR & Expected Development on Reported Claims	$ 22.1
Cumulative Number of Reported Claims | claim	122
International Operations [Member] | Reinsurance Division [Member] | Property [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 798.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	716.9
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	3.7
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	85.7
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	140.5	138.3	131.7	103.7	103.9	104.6	106.7	104.7	126.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	137.4	133.6	126.8	98.6	97.4	95.3	87.8	67.0	41.6
IBNR & Expected Development on Reported Claims	$ 0.3
Cumulative Number of Reported Claims | claim	460
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 69.3	66.9	62.7	46.4	51.6	50.3	51.3	47.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	68.1	64.6	58.7	44.0	49.6	40.5	31.1	12.4
IBNR & Expected Development on Reported Claims	$ 0.0
Cumulative Number of Reported Claims | claim	278
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 31.6	32.1	32.7	31.1	32.8	33.3	31.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	30.8	30.8	30.7	28.7	26.3	16.5	4.1
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	222
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 39.9	38.1	35.3	24.2	26.5	26.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	39.5	37.0	36.4	18.3	12.6	2.8
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative Number of Reported Claims | claim	221
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 150.2	155.1	159.5	23.4	27.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	145.9	142.5	135.4	11.0	4.2
IBNR & Expected Development on Reported Claims	$ 1.3
Cumulative Number of Reported Claims | claim	220
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 58.4	41.1	48.5	43.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	51.6	31.1	27.1	13.5
IBNR & Expected Development on Reported Claims	$ 4.9
Cumulative Number of Reported Claims | claim	384
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 165.1	158.0	157.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	164.0	139.6	84.2
IBNR & Expected Development on Reported Claims	$ (14.5)
Cumulative Number of Reported Claims | claim	813
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 82.7	68.0
Cumulative Paid Losses & ALAE, Net of Reinsurance	71.5	24.6
IBNR & Expected Development on Reported Claims	$ (11.6)
Cumulative Number of Reported Claims | claim	645
International Operations [Member] | Reinsurance Division [Member] | Property [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 61.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	8.1
IBNR & Expected Development on Reported Claims	$ 43.0
Cumulative Number of Reported Claims | claim	133
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 132.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	47.4
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	0.0
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	85.0
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	0.0	0.0	1.0	1.6	2.2	4.4	6.6	6.6	6.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
IBNR & Expected Development on Reported Claims	$ 0.0
Cumulative Number of Reported Claims | claim	1,425
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 0.6	0.0	1.7	4.4	5.6	7.4	7.4	7.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
IBNR & Expected Development on Reported Claims	$ 0.6
Cumulative Number of Reported Claims | claim	1,385
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 5.3	2.2	4.9	8.5	8.5	8.5	8.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	2.3	2.3	2.3	0.0	0.0	0.0	0.0
IBNR & Expected Development on Reported Claims	$ 1.9
Cumulative Number of Reported Claims | claim	1,194
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 2.3	1.5	6.2	9.8	9.8	9.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.2	1.2	0.1	0.1	0.0	0.0
IBNR & Expected Development on Reported Claims	$ 0.3
Cumulative Number of Reported Claims | claim	1,338
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 45.4	35.4	24.8	14.3	11.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	26.6	20.3	16.1	0.0	0.0
IBNR & Expected Development on Reported Claims	$ 6.7
Cumulative Number of Reported Claims | claim	1,583
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 6.6	14.0	14.0	13.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.1	0.0	0.0	0.0
IBNR & Expected Development on Reported Claims	$ 6.5
Cumulative Number of Reported Claims | claim	1,907
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 26.9	17.3	17.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	3.4	3.3	0.0
IBNR & Expected Development on Reported Claims	$ 4.6
Cumulative Number of Reported Claims | claim	2,035
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 32.0	8.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	13.8	0.0
IBNR & Expected Development on Reported Claims	$ 13.7
Cumulative Number of Reported Claims | claim	982
International Operations [Member] | Bermuda Insurance [Member] | Liability [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 13.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.0
IBNR & Expected Development on Reported Claims	$ 13.3
Cumulative Number of Reported Claims | claim	907
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 219.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	126.3	2.3
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	93.3
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	6.2	5.8	5.9	5.8	5.9	6.0	6.2	4.5	4.9	$ 5.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	5.1	4.4	4.1	3.8	2.8	2.0	1.1	0.6	0.2	0.0
IBNR & Expected Development on Reported Claims	0.1
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	11.5	10.9	10.7	10.2	10.4	11.1	11.0	8.7	8.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	9.8	8.8	7.9	7.0	5.5	3.4	1.7	0.8	0.2
IBNR & Expected Development on Reported Claims	0.5
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	15.6	15.0	14.5	13.8	14.2	14.9	10.7	8.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	12.8	11.8	10.0	8.2	5.7	2.5	1.2	0.4
IBNR & Expected Development on Reported Claims	0.6
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	26.4	25.0	24.2	24.3	26.2	26.7	22.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	22.5	19.7	15.6	11.3	7.0	3.2	1.5
IBNR & Expected Development on Reported Claims	1.5
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	35.6	33.5	32.2	33.3	35.9	36.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	24.6	20.1	13.6	9.8	4.5	1.9
IBNR & Expected Development on Reported Claims	3.7
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	32.9	29.1	28.8	29.1	34.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	17.5	12.2	7.3	5.1	0.8
IBNR & Expected Development on Reported Claims	6.5
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	28.3	25.8	26.2	25.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	15.1	10.5	5.7	1.8
IBNR & Expected Development on Reported Claims	7.1
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	26.7	23.2	24.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	11.0	6.6	1.9
IBNR & Expected Development on Reported Claims	11.9
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	19.9	21.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	6.6
IBNR & Expected Development on Reported Claims	12.0
International Operations [Member] | Syndicate 1200 [Member] | Liability [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	16.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.3
IBNR & Expected Development on Reported Claims	13.6
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	243.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	145.3
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	98.2
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	10.0	9.8	9.5	9.5	9.4	10.1	11.2	12.7	12.8	15.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	7.9	7.7	6.8	6.5	5.1	3.8	3.0	2.0	1.0	0.1
IBNR & Expected Development on Reported Claims	0.2
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	16.2	15.7	15.1	14.7	14.6	15.5	18.5	21.0	19.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	13.5	12.8	11.4	10.6	8.3	6.6	4.2	2.5	1.0
IBNR & Expected Development on Reported Claims	0.7
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	16.0	15.1	14.6	13.7	13.6	13.7	13.5	13.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	12.5	11.2	9.5	8.2	5.8	4.3	1.8	0.6
IBNR & Expected Development on Reported Claims	0.8
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	23.9	22.5	21.7	21.5	21.9	21.8	21.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	20.1	17.7	15.4	11.6	7.1	3.7	1.7
IBNR & Expected Development on Reported Claims	2.1
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	41.9	40.0	38.1	35.1	35.0	33.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	32.3	27.8	23.6	14.6	6.3	1.6
IBNR & Expected Development on Reported Claims	4.9
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	40.8	37.4	37.3	36.1	36.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	24.9	19.6	14.8	8.3	2.2
IBNR & Expected Development on Reported Claims	8.6
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	30.9	25.5	26.0	31.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	17.2	10.6	5.8	2.1
IBNR & Expected Development on Reported Claims	8.0
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	24.4	21.1	23.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	9.6	5.0	1.2
IBNR & Expected Development on Reported Claims	11.3
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	17.0	20.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	4.8	1.0
IBNR & Expected Development on Reported Claims	10.6
International Operations [Member] | Syndicate 1200 [Member] | Professional [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	22.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	2.5
IBNR & Expected Development on Reported Claims	18.6
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	700.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	544.2
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	156.1
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	12.0	12.0	12.1	12.1	12.1	12.1	13.1	13.6	15.8	12.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	10.3	10.2	10.1	10.0	9.7	9.0	9.3	8.9	8.6	1.9
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	32.8	32.9	33.2	33.4	33.3	34.2	38.9	40.2	38.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	29.3	29.5	29.6	29.2	28.6	27.2	23.7	19.6	11.5
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	58.0	58.3	58.9	59.1	59.3	60.8	56.4	52.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	50.2	50.2	49.9	48.8	45.8	39.0	27.5	17.9
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	80.7	81.7	82.0	82.3	82.7	81.3	75.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	78.3	78.6	78.3	76.3	68.9	52.5	31.0
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	99.1	100.8	101.4	99.9	98.6	92.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	89.4	90.4	89.0	82.7	71.5	37.8
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	95.0	95.3	93.8	87.8	89.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	75.5	73.9	66.0	54.0	31.0
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	89.5	87.2	83.9	85.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	75.2	68.3	58.6	37.2
IBNR & Expected Development on Reported Claims	2.2
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	85.9	76.0	79.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	57.1	42.2	19.8
IBNR & Expected Development on Reported Claims	7.1
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	69.8	64.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	49.3	18.7
IBNR & Expected Development on Reported Claims	17.5
International Operations [Member] | Syndicate 1200 [Member] | Specialty [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	77.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	29.6
IBNR & Expected Development on Reported Claims	44.7
International Operations [Member] | Syndicate 1200 [Member] | Property [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	735.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	617.3
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	117.9
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2010 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	51.1	51.2	51.5	50.8	51.3	51.6	54.3	54.8	58.2	50.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	43.4	43.4	42.7	41.6	40.1	35.9	33.9	28.1	19.6	$ 1.8
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2011 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	91.9	92.2	92.8	92.7	93.3	95.2	108.0	113.8	108.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	82.0	82.6	82.9	81.3	79.6	73.8	62.0	47.3	$ 23.5
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	89.6	90.1	90.9	91.0	92.1	93.0	88.7	88.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	77.7	77.8	77.6	76.4	74.1	63.0	47.8	29.6
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	74.6	75.7	76.7	76.9	78.3	79.3	83.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	72.5	73.5	74.3	73.5	69.3	56.8	44.5
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	63.6	65.6	66.3	65.7	64.2	69.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	58.0	60.0	60.1	57.6	51.5	29.5
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	72.9	74.2	73.6	66.3	55.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	58.6	59.1	52.7	42.8	22.9
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	90.7	91.6	86.4	70.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	80.0	78.6	63.9	38.9
IBNR & Expected Development on Reported Claims	0.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	96.1	91.4	84.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	71.5	62.4	29.3
IBNR & Expected Development on Reported Claims	3.0
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	61.9	62.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	53.1	30.2
IBNR & Expected Development on Reported Claims	6.2
International Operations [Member] | Syndicate 1200 [Member] | Property [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	42.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	20.5
IBNR & Expected Development on Reported Claims	21.4
International Operations [Member] | Europe [Member] | Professional [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	170.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	27.9
Outstanding liabilities for unpaid losses and ALAE prior to 2011, net of reinsurance	0.0
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	143.0
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2012 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	0.1	0.2	0.1	0.1	0.1	0.0	0.1	0.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.0	0.1	0.0	0.0	0.0	0.0	0.0	$ 0.0
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative Number of Reported Claims | claim	3
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 0.4	0.6	0.5	0.4	0.5	0.7	0.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.2	0.5	0.5	0.4	0.5	0.0	$ 0.0
IBNR & Expected Development on Reported Claims	$ 0.2
Cumulative Number of Reported Claims | claim	22
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 6.7	0.7	0.7	0.5	0.6	0.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.1	0.1	0.1	0.0	0.0	$ 0.0
IBNR & Expected Development on Reported Claims	$ 6.6
Cumulative Number of Reported Claims | claim	19
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 21.1	18.4	2.9	2.1	2.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	2.3	0.1	0.0	0.0	$ 0.0
IBNR & Expected Development on Reported Claims	$ 18.8
Cumulative Number of Reported Claims | claim	36
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 0.8	1.1	1.1	0.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.1	0.3	0.0	$ 0.0
IBNR & Expected Development on Reported Claims	$ 0.7
Cumulative Number of Reported Claims | claim	63
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 13.5	6.1	5.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	6.8	2.0	$ 1.0
IBNR & Expected Development on Reported Claims	$ (10.4)
Cumulative Number of Reported Claims | claim	91
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 56.6	45.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	17.2	$ 9.8
IBNR & Expected Development on Reported Claims	$ 7.6
Cumulative Number of Reported Claims | claim	143
International Operations [Member] | Europe [Member] | Professional [Member] | Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 71.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.2
IBNR & Expected Development on Reported Claims	$ 69.3
Cumulative Number of Reported Claims | claim	101