Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 62.4	$ 42.7
Bermuda [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	25.7	21.9
Effective Tax Rate	0.00%	0.00%
United States [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	28.5	14.8
Effective Tax Rate	20.20%	20.60%
United Kingdom [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	10.1	7.3
Effective Tax Rate	(21.90%)	(7.70%)
Belgium [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	(0.2)	0	[1]
Effective Tax Rate	(4.80%)	18.10%
Brazil [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	(1.9)	0
Effective Tax Rate	0.00%	0.00%
United Arab Emirates [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	0.1	(0.9)
Effective Tax Rate	0.00%	0.00%
Ireland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	(0.2)	0
Effective Tax Rate	0.00%	0.00%
Malta [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	0.3	(0.4)
Effective Tax Rate	0.00%	0.00%
Switzerland [Member]
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	[1]
Effective Tax Rate	21.00%	(19.80%)

[1] Pre-tax income for the respective year was less than $0.1 million.