Assets Measured At Fair Value On Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	$ 12,308,684	$ 11,888,205	[1]
Equity securities	16,820	17,056	[1]
Total fixed maturities and equity securities	12,325,504
Percent of total	100.00%
U.S. Government Direct, Guaranteed, And Government-Sponsored Enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	31,141
Total fixed maturities and equity securities	31,141
States, Municipalities, And Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	1,372,605
Total fixed maturities and equity securities	1,372,605
Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	22,873
Total fixed maturities and equity securities	22,873
Corporates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	9,697,066
Total fixed maturities and equity securities	9,697,066
Collateralized Debt Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	29,957
Total fixed maturities and equity securities	29,957
Other Asset-Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	38,390
Total fixed maturities and equity securities	38,390
Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	1,116,652
Total fixed maturities and equity securities	1,116,652
Total Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	12,308,684
Total fixed maturities and equity securities	12,308,684
Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	16,820
Total fixed maturities and equity securities	16,820
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities and equity securities	252,146
Percent of total	2.10%
Fair Value, Inputs, Level 1 | U.S. Government Direct, Guaranteed, And Government-Sponsored Enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 1 | States, Municipalities, And Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 1 | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 1 | Corporates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	43,498
Fair Value, Inputs, Level 1 | Collateralized Debt Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 1 | Other Asset-Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 1 | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	192,653
Fair Value, Inputs, Level 1 | Total Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	236,151
Fair Value, Inputs, Level 1 | Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	15,995
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities and equity securities	11,996,629
Percent of total	97.30%
Fair Value, Inputs, Level 2 | U.S. Government Direct, Guaranteed, And Government-Sponsored Enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	31,141
Fair Value, Inputs, Level 2 | States, Municipalities, And Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	1,372,605
Fair Value, Inputs, Level 2 | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	22,873
Fair Value, Inputs, Level 2 | Corporates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	9,614,687
Fair Value, Inputs, Level 2 | Collateralized Debt Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 2 | Other Asset-Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	31,238
Fair Value, Inputs, Level 2 | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	923,999
Fair Value, Inputs, Level 2 | Total Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	11,996,543
Fair Value, Inputs, Level 2 | Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	86
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total fixed maturities and equity securities	76,729
Percent of total	0.60%
Fair Value, Inputs, Level 3 | U.S. Government Direct, Guaranteed, And Government-Sponsored Enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 3 | States, Municipalities, And Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 3 | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 3 | Corporates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	38,881
Fair Value, Inputs, Level 3 | Collateralized Debt Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	29,957
Fair Value, Inputs, Level 3 | Other Asset-Backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	7,152
Fair Value, Inputs, Level 3 | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0
Fair Value, Inputs, Level 3 | Total Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	75,990
Fair Value, Inputs, Level 3 | Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	$ 739

[1] Derived from audited financial statements. Additionally, 2011 balances have been retrospectively adjusted to give effect to the adoption of new accounting guidance as described in Note F-Adoption of New Accounting Standard.