Quantitative Information about Level Three Fair Value Measurements (Detail) (USD $) In Thousands, unless otherwise specified				12 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Fair Value, Inputs, Level 3	Dec. 31, 2012 Fair Value, Inputs, Level 3 Collateralized Debt Obligations Discounted Cash Flows Valuation Technique	Dec. 31, 2012 Fair Value, Inputs, Level 3 Private Placement Bonds Discounted Cash Flows Valuation Technique	Dec. 31, 2012 Fair Value, Inputs, Level 3 Other Investments Third-party Pricing Without Adjustment	Dec. 31, 2012 Fair Value, Inputs, Level 3 Weighted Average Collateralized Debt Obligations Discounted Cash Flows Valuation Technique
Quantitative Information About Significant Unobservable Inputs [Line Items]
Fair value fixed maturities measured on recurring basis	$ 13,541,193	$ 11,888,205	$ 286,363	$ 46,571	$ 182,946	$ 56,846
Discount rate				15.00%			15.00%