v2.4.0.6
Amortized Cost, Estimated Market Value and Gross Unrealized Appreciation and Depreciation of Available-for-sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Jun. 30, 2012
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost $ 1,799,566
Gross unrealized gains 75,859
Gross unrealized losses (23,836)
Market value 1,851,589
Preferred stock
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 5,091
Gross unrealized gains 57
Gross unrealized losses (289)
Market value 4,859
Common stock
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 20,904
Gross unrealized gains 2,238
Gross unrealized losses (2,171)
Market value 20,971
U.S. treasury securities
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 44,087
Gross unrealized gains 2,781
Gross unrealized losses (5)
Market value 46,863
U.S. government agencies
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 53,619
Gross unrealized gains 762
Market value 54,381
Municipal bonds
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 261,865
Gross unrealized gains 11,274
Gross unrealized losses (87)
Market value 273,052
Commercial mortgage backed securities
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 10,015
Gross unrealized gains 103
Market value 10,118
Agency, residential mortgage backed securities
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 346,956
Gross unrealized gains 20,794
Gross unrealized losses (320)
Market value 367,430
Non-agency, residential mortgage backed securities
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 7,950
Gross unrealized gains 2
Gross unrealized losses (728)
Market value 7,224
Corporate bonds | Finance
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 744,393
Gross unrealized gains 26,438
Gross unrealized losses (16,202)
Market value 754,629
Corporate bonds | Industrial
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 266,459
Gross unrealized gains 9,407
Gross unrealized losses (3,105)
Market value 272,761
Corporate bonds | Utilities
 
Schedule of Available-for-sale Securities [Line Items]  
Original or amortized cost 38,227
Gross unrealized gains 2,003
Gross unrealized losses (929)
Market value $ 39,301