v2.4.0.8
Investments - Contractual Maturities (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2014
Dec. 31, 2013
Schedule of Investments [Line Items]    
Due in one year or less, Amortized cost $ 54,893  
Due after one year through five years, Amortized cost 422,796  
Due after five years through ten years, Amortized cost 1,226,383  
Due after ten years, Amortized cost 91,606  
Total before securities without single maturities, Amortized cost 1,795,678  
Total Amortized cost 3,096,675  
Due in one year or less, Fair value 56,249  
Due after one year through five years, Fair value 459,480  
Due after five years through ten years, Fair value 1,277,651  
Due after ten years, Fair value 95,601  
Total before securities without single maturities, Fair value 1,888,981  
Fair value 3,168,819 3,162,067
Due in one year or less, % of Total fair value 1.80%  
Due after one year through five years, % of Total fair value 14.50%  
Due after five years through ten years, % of Total fair value 40.30%  
Due after ten years, % of Total fair value 3.00%  
Total before securities without single maturities, % of Total fair value 59.60%  
% of Total fair value 100.00% 100.00%
U.S. agency bonds – mortgage-backed [Member]
    
Schedule of Investments [Line Items]    
Amortized cost of securities without single maturities 1,257,045  
Fair value of securities without single maturities 1,235,470  
Fair value 1,235,470 1,262,655
% of Total fair value for securities without single maturities 39.00%  
Other mortgage-backed securities [Member]
    
Schedule of Investments [Line Items]    
Amortized cost of securities without single maturities 43,952  
Fair value of securities without single maturities 44,368  
Fair value $ 44,368 $ 33,444
% of Total fair value for securities without single maturities 1.40%