Reinsurance Recoverables (Detail) (USD $)	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011		Dec. 31, 2010
Ceded Credit Risk [Line Items]
Reinsurance recoverables on paid losses	$ 39,300,000		$ 21,000,000
Ceded outstanding loss and LAE	1,232,300,000	[1]	831,800,000	[1]	840,800,000	[1]	847,400,000	[1]
Total reinsurance recoverables	$ 1,271,555,000	[2]	$ 852,845,000

[1] Reinsurance recoverables in this table include only ceded loss reserves.

[2] Reinsurance recoverables reflect amounts due from one or more reinsurance subsidiaries of the listed company.