Reinsurance Ceded - Additional Information (Detail) (RSUI, USD $) In Millions, unless otherwise specified	3 Months Ended	0 Months Ended
	Mar. 31, 2015	May 01, 2015
Effects of Reinsurance [Line Items]
Description of reinsurance program	The catastrophe reinsurance program provides coverage for $600.0 million of losses in excess of a $200.0 million net retention after application of 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. The first and second layers of coverage include terms as follows: 34.0 percent of coverage limits will expire on April 30, 2016, 33.0 percent of coverage limits will expire on April 30, 2017, and 33.0 percent of coverage limits will expire on April 30, 2018. The third layer of coverage will expire on April 30, 2017. In addition, RSUI’s property per risk reinsurance program runs on an annual basis from May 1 to the following April 30 and thus expired on April 30, 2015. On May 1, 2015, the property per risk program was renewed and will expire on April 30, 2016. For the 2015 to 2016 period, RSUI’s property per risk reinsurance program provides 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 surplus share treaties and facultative reinsurance.
Subsequent Event | Current Catastrophe Reinsurance Program
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation		$ 600.0
Net retention		200.0
Subsequent Event | 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%
Subsequent Event | Current Catastrophe Reinsurance Program | Layer 2
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation		100.0
Net retention		500.0
Subsequent Event | Current Catastrophe Reinsurance Program | Layer 3
Effects of Reinsurance [Line Items]
Reinsurance coverage before co-participation		200.0
Net retention		600.0
Reinsurance coverage expiration date		Apr. 30, 2017
Subsequent Event | Current Catastrophe Reinsurance Program | Layer 1 And 2 | Period 1
Effects of Reinsurance [Line Items]
Reinsurance percentage of coverage		34.00%
Reinsurance coverage expiration date		Apr. 30, 2016
Subsequent Event | Current Catastrophe Reinsurance Program | Layer 1 And 2 | Period 2
Effects of Reinsurance [Line Items]
Reinsurance percentage of coverage		33.00%
Reinsurance coverage expiration date		Apr. 30, 2017
Subsequent Event | Current Catastrophe Reinsurance Program | Layer 1 And 2 | Period 3
Effects of Reinsurance [Line Items]
Reinsurance percentage of coverage		33.00%
Reinsurance coverage expiration date		Apr. 30, 2018
Subsequent Event | 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%
Reinsurance coverage expiration date		Apr. 30, 2016