Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable (Parenthetical) (Detail) (USD $)	Sep. 30, 2014
Ceded Credit Risk [Line Items]
Reserve for uncollectible reinsurance amount	$ 11,300,000
Collateral Held	217,161,000	[1]
Ceded Balances Payable
Ceded Credit Risk [Line Items]
Collateral Held	157,900,000
Letter of Credit
Ceded Credit Risk [Line Items]
Collateral Held	53,400,000
All Other
Ceded Credit Risk [Line Items]
Collateral Held	$ 5,900,000

[1] Collateral of $217.2 million consists of $157.9 million in ceded balances payable, $53.4 million in letters of credit, and $5.9 million of other balances held by the Company's Insurance Companies and Lloyd's Operations.