Reinsurance Ceded - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014 Entity	Jun. 30, 2013	Jun. 30, 2014 Entity	Jun. 30, 2013
Effects of Reinsurance [Line Items]
Ceded premiums earned	$ 115.5	$ 115.3	$ 229.1	$ 226.3
Ceded losses incurred	$ 57.9	$ 77.6	$ 111.8	$ 131.1
Percentage of reinsurance recoverable of 20 largest reinsurers			76.60%
Number of largest reinsurers	20		20