Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 28.2	$ (26.5)	$ 138.1	$ (46.3)
Effective Tax Rate	20.60%	12.90%	11.70%	(14.80%)
Bermuda
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 7.2	$ 5.5	$ 14.5	$ (49.1)
Effective Tax Rate	0.00%	0.10%	0.00%	0.00%
United States
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 21.4	$ 7.2	$ 126.7	$ 62.5
Effective Tax Rate	26.80%	3.10%	20.70%	21.30%
United Kingdom
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (6.1)	$ (38.1)	$ (14.9)	$ (65.7)
Effective Tax Rate	(1.00%)	9.70%	68.40%	9.90%
Barbados
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Belgium
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.2	$ 0.0	$ 0.2
Effective Tax Rate	0.00%	22.80%	0.00%	25.30%
Brazil
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 5.9	$ 0.3	$ 9.8	$ 3.2
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United Arab Emirates
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.9	$ 0.4	$ 1.2	$ 1.8
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Ireland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.0	$ (0.1)	$ (0.1)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Italy
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.2	$ (0.9)	$ 1.4	$ 0.7
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Malta
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (1.3)	$ (1.1)	$ (0.4)	$ 0.2
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Switzerland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.0	$ (0.1)	$ 0.0
Effective Tax Rate	0.00%	1.00%	0.00%	0.00%