Lists of 20 Largest Reinsurers Measured by Reinsurance Recoverable (Parenthetical) (Detail) (USD $)	Mar. 31, 2014
Ceded Credit Risk [Line Items]
Reserve for uncollectible reinsurance amount	$ 11,300,000
Collateral Held	205,440,000	[1]
Ceded Balances Payable
Ceded Credit Risk [Line Items]
Collateral Held	145,900,000
Letter of Credit
Ceded Credit Risk [Line Items]
Collateral Held	53,400,000
All Other
Ceded Credit Risk [Line Items]
Collateral Held	$ 6,100,000

[1] Collateral of $205.4 million consists of $145.9 million in ceded balances payable, $53.4 million in letters of credit, and $6.1 million of other balances held by the Company's Insurance Companies and Lloyd's Operations.