Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 100.1	$ 25.0
Effective Tax Rate	8.90%	0.70%
Bermuda [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 32.0	$ 25.3
Effective Tax Rate	0.00%	0.00%
United States [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 69.4	$ (6.3)
Effective Tax Rate	14.40%	23.00%
United Kingdom [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (3.5)	$ 6.2
Effective Tax Rate	31.50%	24.50%
Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.1
Effective Tax Rate	30.80%	35.80%
Brazil [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 1.8	$ (1.4)
Effective Tax Rate	0.00%	0.00%
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.2	$ 0.2
Effective Tax Rate	0.00%	0.00%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.0
Effective Tax Rate	0.00%	0.00%
Italy [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (0.7)	$ 0.0
Effective Tax Rate	0.00%	0.00%
Malta [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.9	$ 0.9
Effective Tax Rate	0.00%	0.00%
Luxembourg [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.0
Effective Tax Rate	0.00%	0.00%
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.0	$ 0.0
Effective Tax Rate	0.00%	21.20%