Valuation and Qualifying Accounts (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Allowance for uncollectable reinsurance
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at January 1, 2012	$ 13,020
Charged (Credited) to Costs and Expenses	(1,500)
Charged to Other Accounts
Deductions (Describe)
Balance at December 31, 2012	11,520
Valuation allowance in deferred taxes
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at January 1, 2012	242
Charged (Credited) to Costs and Expenses	257
Charged to Other Accounts
Deductions (Describe)
Balance at December 31, 2012	$ 499