Reinsurance - Additional Information (Detail)	6 Months Ended
Jun. 30, 2011
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Description of reinsurance program	As discussed in the 2010 10-K, RSUI reinsures its property lines of business through a program consisting of surplus share treaties, facultative placements, per risk and catastrophe excess of loss treaties. RSUI’s catastrophe reinsurance program (which covers catastrophe risks including, among others, windstorms and earthquakes) and per risk reinsurance program run on an annual basis from May 1 to the following April 30 and thus expired on April 30, 2011. RSUI renewed all of its catastrophe reinsurance program for the 2011-2012 period, and the new reinsurance program is similar to the expired program. The new reinsurance program provides coverage in two layers for $400.0 million of losses in excess of a $100.0 million net retention after application of the surplus share treaties, facultative reinsurance and per risk covers. The first layer provides coverage for $100.0 million of losses, before a 47.0 percent co-participation by RSUI (compared with a 33.0 percent co-participation under the expired program), in excess of the $100.0 million net retention, and the second layer provides coverage for $300.0 million of losses, before a 5.0 percent co-participation by RSUI, in excess of $200.0 million. In addition, RSUI’s property per risk reinsurance program for the 2011-2012 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. As discussed in Note 5(a) to the Notes to Consolidated Financial Statements set forth in Item 8 of the 2010 10-K, RSUI reinsures its other lines of business through quota share treaties, except for professional liability, binding authority and (effective April 15, 2011) the general liability lines where RSUI retains all of such business. RSUI’s quota share reinsurance treaty for umbrella/excess lines of business renewed on June 1, 2011 on the same terms as the expiring treaty, providing coverage for policies with limits up to $30.0 million, with RSUI ceding 35.0 percent of the premium and loss for policies with limits up to $15.0 million and ceding 67.5 percent of the premium and loss for policies with limits in excess of $15.0 million up to $30.0 million. RSUI’s directors and officers liability line quota share reinsurance treaty renewed on July 1, 2011 on the same terms as the expiring treaty, providing coverage for policies with limits up to $20.0 million, with RSUI ceding 35.0 percent of the premium and loss for policies with limits up to $10.0 million and ceding 60.0 percent of the premium and loss for policies with limits in excess of $10.0 million up to $20.0 million.

Reinsurance - Additional Information (Detail)

6 Months Ended

Jun. 30, 2011

Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]

As discussed in the 2010 10-K, RSUI reinsures its property lines of business through a program consisting of surplus share treaties, facultative placements, per risk and catastrophe excess of loss treaties. RSUI’s catastrophe reinsurance program (which covers catastrophe risks including, among others, windstorms and earthquakes) and per risk reinsurance program run on an annual basis from May 1 to the following April 30 and thus expired on April 30, 2011. RSUI renewed all of its catastrophe reinsurance program for the 2011-2012 period, and the new reinsurance program is similar to the expired program. The new reinsurance program provides coverage in two layers for $400.0 million of losses in excess of a $100.0 million net retention after application of the surplus share treaties, facultative reinsurance and per risk covers. The first layer provides coverage for $100.0 million of losses, before a 47.0 percent co-participation by RSUI (compared with a 33.0 percent co-participation under the expired program), in excess of the $100.0 million net retention, and the second layer provides coverage for $300.0 million of losses, before a 5.0 percent co-participation by RSUI, in excess of $200.0 million. In addition, RSUI’s property per risk reinsurance program for the 2011-2012 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. As discussed in Note 5(a) to the Notes to Consolidated Financial Statements set forth in Item 8 of the 2010 10-K, RSUI reinsures its other lines of business through quota share treaties, except for professional liability, binding authority and (effective April 15, 2011) the general liability lines where RSUI retains all of such business. RSUI’s quota share reinsurance treaty for umbrella/excess lines of business renewed on June 1, 2011 on the same terms as the expiring treaty, providing coverage for policies with limits up to $30.0 million, with RSUI ceding 35.0 percent of the premium and loss for policies with limits up to $15.0 million and ceding 67.5 percent of the premium and loss for policies with limits in excess of $15.0 million up to $30.0 million. RSUI’s directors and officers liability line quota share reinsurance treaty renewed on July 1, 2011 on the same terms as the expiring treaty, providing coverage for policies with limits up to $20.0 million, with RSUI ceding 35.0 percent of the premium and loss for policies with limits up to $10.0 million and ceding 60.0 percent of the premium and loss for policies with limits in excess of $10.0 million up to $20.0 million.