Accumulated Balances Related to Each Component of Accumulated Other Comprehensive Income (Detail) (USD $)
 3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Other Comprehensive Income [Line Items]        
Net Unrealized Gain (Loss) on Non-Impaired Securities, Beginning Balance     $ 213,800,000  
Other Comprehensive Income, Net Unrealized Gain (Loss) on Non-Impaired Securities     65,031,000  
Net Unrealized Gain (Loss) on Non-Impaired Securities, Ending Balance 278,831,000   278,831,000  
Net unrealized gain (loss) on impaired securities, Beginning balance     (15,612)  
Other Comprehensive Income, Net unrealized gain (loss) on impaired securities     14,423  
Net unrealized gain (loss) on impaired securities, Ending balance (1,189)   (1,189)  
Benefit Plan Obligations, Beginning Balance     (78,451,000)  
Other comprehensive income, Benefit Plan Obligations         
Benefit Plan Obligations, Ending Balance (78,451,000)   (78,451,000)  
DAC\VOBA Impact, Beginning Balance     (56,971,000)  
Other Comprehensive Income, DAC\VOBA Impact (6,585,000) (20,189,000) (17,839,000) (27,019,000)
DAC\VOBA Impact, Ending Balance (74,810,000)   (74,810,000)  
Future policy benefits, Beginning Balance     (15,903,000)  
Other comprehensive income, Future policy benefits (5,564,000) (5,940,000) (13,209,000) (9,335,000)
Future policy benefits, Ending Balance (29,112,000)   (29,112,000)  
Policyholder Account, Beginning Balance     (578,000)  
Other comprehensive income, Policyholder Account Balances (274,000) (148,000) (609,000) (265,000)
Policyholder Account, Ending Balance (1,187,000)   (1,187,000)  
Tax Effect, Beginning Balance     (16,199,000)  
Other comprehensive income, Tax Effect (9,821,000) (10,941,000) (16,729,000) (20,037,000)
Tax Effect, Ending Balance (32,928,000)   (32,928,000)  
Beginning of year, Total     30,086,000  
Other comprehensive income 18,238,000 20,312,000 31,068,000 37,207,000
End of period, Total $ 61,154,000   $ 61,154,000