v3.3.1.900
Investments - Credit Ratings (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of Fixed Maturities [Line Items]      
OTTI recognized through earnings $ (1,060) $ (2,364) $ 0
Amortized cost 4,170,707 3,379,864  
Fair value $ 4,107,063 $ 3,456,904  
% of Total fair value 100.00% 100.00%  
U.S. treasury bonds      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 5,714 $ 8,937  
Fair value $ 6,010 $ 9,360  
% of Total fair value 0.10% 0.30%  
U.S. agency bonds      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 1,495,516 $ 1,321,047  
Fair value $ 1,501,302 $ 1,330,431  
% of Total fair value 36.60% 38.50%  
AAA      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 170,190 $ 193,280  
Fair value $ 170,391 $ 202,973  
% of Total fair value 4.10% 5.90%  
AA Plus, AA, AA Minus      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 222,506 $ 116,936  
Fair value $ 223,084 $ 120,679  
% of Total fair value 5.40% 3.50%  
A Plus, A, A Minus      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 1,075,550 $ 883,092  
Fair value $ 1,066,794 $ 917,544  
% of Total fair value 26.00% 26.50%  
BBB Plus, BBB, BBB Minus      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 1,077,064 $ 794,244  
Fair value $ 1,039,228 $ 814,039  
% of Total fair value 25.30% 23.50%  
BB Plus or Lower      
Schedule of Fixed Maturities [Line Items]      
Amortized cost $ 124,167 $ 62,328  
Fair value $ 100,254 $ 61,878  
% of Total fair value 2.50% 1.80%