Segment Information (Schedule Of Earned Premiums By Geographic Location) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Total earned premiums	$ 304.3	$ 270.9	$ 871.8	$ 804.0
Bermuda [Member]
Segment Reporting Information [Line Items]
Total earned premiums	32.6	21.2	83.5	76.3
Brazil [Member]
Segment Reporting Information [Line Items]
Total earned premiums	6.7	0	18.4	0
Malta [Member]
Segment Reporting Information [Line Items]
Total earned premiums	0	0	0.1	0
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total earned premiums	84.9	67.3	231.1	188.2
United States [Member]
Segment Reporting Information [Line Items]
Total earned premiums	$ 180.1	$ 182.4	$ 538.7	$ 539.5