Reinsurance Ceded - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014 Entity	Sep. 30, 2013	Sep. 30, 2014 Entity	Sep. 30, 2013
Effects of Reinsurance [Line Items]
Ceded premiums earned	$ 107.6	$ 114.2	$ 336.7	$ 340.5
Ceded losses incurred	$ 58.7	$ (37.0)	$ 170.4	$ 94.1
Percentage of reinsurance recoverable of 20 largest reinsurers			76.60%
Number of largest reinsurers	20		20