Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable (Parenthetical) (Detail) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Ceded Credit Risk [Line Items]
Reserve for uncollectible reinsurance amount	$ 11,300,000		$ 11,500,000
Collateral Held	223,477,000	[1]
Ceded Balances Payable
Ceded Credit Risk [Line Items]
Collateral Held	167,300,000
Letter of Credit
Ceded Credit Risk [Line Items]
Collateral Held	53,400,000
All Other
Ceded Credit Risk [Line Items]
Collateral Held	$ 2,800,000

[1] Collateral of $223.5 million consists of $167.3 million in ceded balances payable, $53.4 million in letters of credit, and $2.8 million of other balances held by the Company's Insurance Companies and Lloyd's Operations.