Reinsurance Ceded - Additional Information (Detail) (Subsequent Event, RSUI, USD $) In Millions, unless otherwise specified	0 Months Ended
	May 01, 2014
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, before 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. In addition, RSUI’s property per risk reinsurance program for the 2014-2015 period provides RSUI with coverage for $90.0 million of losses, before 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.
Current Catastrophe Reinsurance Program
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation	$ 600.0
Net retention	200.0
Current Catastrophe Reinsurance Program | Layer 1
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation	300.0
Net retention	200.0
Percentage of co-participation	5.00%
Current Catastrophe Reinsurance Program | Layer 2
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation	100.0
Net retention	500.0
Current Catastrophe Reinsurance Program | Layer 3
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation	200.0
Net retention	600.0
Property Per Risk
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation	90.0
Net retention	$ 10.0
Percentage of co-participation	10.00%