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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (26.2)	$ 45.3	$ 103.5	$ 127.4
Effective Tax Rate	4.10%	10.20%	8.40%	15.80%
Bermuda [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (7.8)	$ 6.4	$ 39.1	$ (1.8)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United States [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 7.7	$ 34.8	$ 99.5	$ 114.2
Effective Tax Rate	16.40%	13.40%	14.60%	15.60%
United Kingdom [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (17.9)	$ 3.5	$ (30.3)	$ 16.3
Effective Tax Rate	13.10%	(5.00%)	19.20%	12.30%
Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (0.1)	$ 0.0	$ (0.4)	$ 0.0
Effective Tax Rate	28.60%	30.80%	29.40%	33.30%
Brazil [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 1.2	$ 0.4	$ 5.0	$ (1.0)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.2	$ 0.3	$ 0.5
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ (0.1)	$ (0.1)	$ (0.2)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Italy [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (3.6)	$ (1.8)	$ (4.1)	$ (2.9)
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Malta [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (5.6)	$ 1.8	$ (5.4)	$ 2.2
Effective Tax Rate	0.00%	0.00%	0.00%	0.00%
Luxembourg [Member]
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%
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (0.1)	$ 0.1	$ (0.1)	$ 0.1
Effective Tax Rate	1.00%	21.20%	0.90%	21.20%