Schedule of Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value $ 2,916,078 $ 2,718,831
Percent of total 100.00% 100.00%
Other policyholder funds
   
Schedule of Available-for-sale Securities [Line Items]    
Liabilities, Fair Value (409) (187)
Corporate obligations
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,172,405 1,970,886
Equity securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 37,453 36,689
GMWB | Other policyholder funds
   
Schedule of Available-for-sale Securities [Line Items]    
Liabilities, Fair Value (409) (187)
Fixed maturity securities available for sale
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,878,625 2,682,142
Fixed maturity securities available for sale | US treasury securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 265,996 279,955
Fixed maturity securities available for sale | U.S. Treasury securities and obligations of U.S. Government
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 138,511 134,437
Fixed maturity securities available for sale | Federal agencies
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 26,250 [1] 25,881 [1]
Fixed maturity securities available for sale | Federal agency issued residential mortgage-backed securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 101,235 [1] 119,637 [1]
Fixed maturity securities available for sale | Corporate obligations | Industrial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 554,550 486,880
Fixed maturity securities available for sale | Corporate obligations | Energy
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 206,712 171,711
Fixed maturity securities available for sale | Corporate obligations | Communications and technology
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 225,310 201,393
Fixed maturity securities available for sale | Corporate obligations | Financial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 328,837 318,078
Fixed maturity securities available for sale | Corporate obligations | Consumer
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 560,544 496,487
Fixed maturity securities available for sale | Corporate obligations | Public utilities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 296,452 296,337
Fixed maturity securities available for sale | Corporate private-labeled residential mortgage-backed securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 154,567 156,902
Fixed maturity securities available for sale | Municipal securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 174,366 168,522
Fixed maturity securities available for sale | Other
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 102,080 94,656
Fixed maturity securities available for sale | Redeemable preferred stocks
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 9,211 11,221
Level 1
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 38,643 26,313
Percent of total 1.00% 1.00%
Level 1 | Corporate obligations
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 14,470  
Level 1 | Equity securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,172 2,216
Level 1 | Fixed maturity securities available for sale
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 36,471 24,097
Level 1 | Fixed maturity securities available for sale | US treasury securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 12,790 12,876
Level 1 | Fixed maturity securities available for sale | U.S. Treasury securities and obligations of U.S. Government
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 12,790 12,876
Level 1 | Fixed maturity securities available for sale | Corporate obligations | Industrial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,900  
Level 1 | Fixed maturity securities available for sale | Corporate obligations | Energy
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,500  
Level 1 | Fixed maturity securities available for sale | Corporate obligations | Financial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,000  
Level 1 | Fixed maturity securities available for sale | Corporate obligations | Consumer
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 4,070  
Level 1 | Fixed maturity securities available for sale | Corporate obligations | Public utilities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 3,000  
Level 1 | Fixed maturity securities available for sale | Redeemable preferred stocks
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 9,211 11,221
Level 2
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,824,434 2,647,636
Percent of total 97.00% 97.00%
Level 2 | Corporate obligations
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,115,729 1,935,469
Level 2 | Equity securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 34,072 33,350
Level 2 | Fixed maturity securities available for sale
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,790,362 2,614,286
Level 2 | Fixed maturity securities available for sale | US treasury securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 250,177 263,648
Level 2 | Fixed maturity securities available for sale | U.S. Treasury securities and obligations of U.S. Government
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 122,692 118,130
Level 2 | Fixed maturity securities available for sale | Federal agencies
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 26,250 [1] 25,881 [1]
Level 2 | Fixed maturity securities available for sale | Federal agency issued residential mortgage-backed securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 101,235 [1] 119,637 [1]
Level 2 | Fixed maturity securities available for sale | Corporate obligations | Industrial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 549,206 486,380
Level 2 | Fixed maturity securities available for sale | Corporate obligations | Energy
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 201,853 169,342
Level 2 | Fixed maturity securities available for sale | Corporate obligations | Communications and technology
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 225,310 201,393
Level 2 | Fixed maturity securities available for sale | Corporate obligations | Financial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 315,303 307,464
Level 2 | Fixed maturity securities available for sale | Corporate obligations | Consumer
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 530,605 474,553
Level 2 | Fixed maturity securities available for sale | Corporate obligations | Public utilities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 293,452 296,337
Level 2 | Fixed maturity securities available for sale | Corporate private-labeled residential mortgage-backed securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 154,567 156,902
Level 2 | Fixed maturity securities available for sale | Municipal securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 170,003 163,611
Level 2 | Fixed maturity securities available for sale | Other
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 99,886 94,656
Level 3
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 53,001 44,882
Percent of total 2.00% 2.00%
Level 3 | Other policyholder funds
   
Schedule of Available-for-sale Securities [Line Items]    
Liabilities, Fair Value (409) (187)
Level 3 | Corporate obligations
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 42,206 35,417
Level 3 | Equity securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 1,209 1,123
Level 3 | GMWB | Other policyholder funds
   
Schedule of Available-for-sale Securities [Line Items]    
Liabilities, Fair Value (409) (187)
Level 3 | Fixed maturity securities available for sale
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 51,792 43,759
Level 3 | Fixed maturity securities available for sale | US treasury securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 3,029 3,431
Level 3 | Fixed maturity securities available for sale | U.S. Treasury securities and obligations of U.S. Government
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 3,029 3,431
Level 3 | Fixed maturity securities available for sale | Corporate obligations | Industrial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,444 500
Level 3 | Fixed maturity securities available for sale | Corporate obligations | Energy
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 2,359 2,369
Level 3 | Fixed maturity securities available for sale | Corporate obligations | Financial
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 11,534 10,614
Level 3 | Fixed maturity securities available for sale | Corporate obligations | Consumer
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 25,869 21,934
Level 3 | Fixed maturity securities available for sale | Municipal securities
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value 4,363 4,911
Level 3 | Fixed maturity securities available for sale | Other
   
Schedule of Available-for-sale Securities [Line Items]    
Securities Fair Value $ 2,194  
[1] Federal agency securities are not backed by the full faith and credit of the U.S. Government.