Investments - Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 28, 2012
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	$ 12,879,133	$ 13,541,193
Equity securities	1,884	15,567
Total fixed maturities and equity securities	12,881,017	13,556,760	13,556,760
Percent of total	100.00%	100.00%
Fixed Maturities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	12,879,133	13,541,193
Fixed Maturities [Member] | U.S. Government Direct, Guaranteed, and Government-Sponsored Enterprises [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	353,173	490,103
Fixed Maturities [Member] | States, Municipalities, and Political Subdivisions [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	1,335,304	1,457,343
Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	44,155	34,565
Fixed Maturities [Member] | Corporates [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	10,536,346	10,697,023
Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	58,205	46,571
Fixed Maturities [Member] | Other Asset-backed Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	38,169	46,867
Fixed Maturities [Member] | Redeemable Preferred Stocks [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	513,781	768,721
Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Equity securities	1,884	15,567
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Total fixed maturities and equity securities	70,386	175,277
Percent of total	0.50%	1.30%
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	69,278	160,449
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | U.S. Government Direct, Guaranteed, and Government-Sponsored Enterprises [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | States, Municipalities, and Political Subdivisions [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | Corporates [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	47,058	31,976
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | Other Asset-backed Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Maturities [Member] | Redeemable Preferred Stocks [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	22,220	128,473
Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Equity securities	1,108	14,828
Fair Value, Inputs, Level 2 [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Total fixed maturities and equity securities	12,451,350	13,095,120
Percent of total	96.70%	96.60%
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	12,451,350	13,095,120
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | U.S. Government Direct, Guaranteed, and Government-Sponsored Enterprises [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	353,173	490,103
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | States, Municipalities, and Political Subdivisions [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	1,335,304	1,457,343
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	44,155	34,565
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | Corporates [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	10,188,988	10,443,526
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | Other Asset-backed Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	38,169	38,886
Fair Value, Inputs, Level 2 [Member] | Fixed Maturities [Member] | Redeemable Preferred Stocks [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	491,561	630,697
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Equity securities	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	359,281
Total fixed maturities and equity securities	359,281	286,363
Percent of total	2.80%	2.10%
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	358,505	285,624
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | U.S. Government Direct, Guaranteed, and Government-Sponsored Enterprises [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | States, Municipalities, and Political Subdivisions [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Foreign Governments [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	0
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Corporates [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	300,300	221,521
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	58,205	46,571
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Other Asset-backed Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	7,981
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member] | Redeemable Preferred Stocks [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Fair value fixed maturities measured on recurring basis	0	9,551
Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis [Line Items]
Equity securities	$ 776	$ 739