Reinsurance Ceded - Additional Information (Detail) (RSUI, USD $) In Millions, unless otherwise specified	9 Months Ended	0 Months Ended
	Sep. 30, 2014	Apr. 30, 2014 Current Catastrophe Reinsurance Program	Apr. 30, 2014 Current Catastrophe Reinsurance Program Layer 1	Apr. 30, 2014 Current Catastrophe Reinsurance Program Layer 2	Apr. 30, 2014 Current Catastrophe Reinsurance Program Layer 3	Apr. 30, 2014 Property Per Risk
Effects of Reinsurance [Line Items]
Description of reinsurance program	The new catastrophe reinsurance program provides coverage in three layers for $600.0 million of losses in excess of a $200.0 million net retention after application of the surplus share treaties and facultative reinsurance. The first layer provides coverage for $300.0 million of losses, subject to a 5.0 percent co-participation by RSUI, in excess of $200.0 million, the second layer provides coverage for $100.0 million of losses in excess of $500.0 million, with no co-participation by RSUI, and the third layer provides coverage for $200.0 million of losses in excess of $600.0 million, with no co-participation by RSUI. In addition, RSUI’s property per risk reinsurance program for the 2014 to 2015 period provides RSUI with coverage for $90.0 million of losses, subject to a 10.0 percent co-participation by RSUI, in excess of a $10.0 million net retention per risk after application of the surplus share treaties and facultative reinsurance.
Reinsurance coverage before co-participation		$ 600.0	$ 300.0	$ 100.0	$ 200.0	$ 90.0
Net retention		$ 200.0	$ 200.0	$ 500.0	$ 600.0	$ 10.0
Percentage of co-participation			5.00%			10.00%