v3.3.1.900
Investments - Contractual Maturities (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]    
Due in one year or less $ 181,769  
Due after one year through five years 477,902  
Due after five years through ten years 1,238,535  
Due after ten years 27,157  
Total before securities with single maturities, Amortized cost 1,925,363  
Amortized Cost 3,562,864 $ 3,379,864
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Due in one year or less 180,407  
Due after one year through five years 475,103  
Due after five years through ten years 1,180,221  
Due after ten years 29,562  
Total before securities with single maturities, Fair value 1,865,293  
Fair value 3,508,088 3,456,904
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Due in one year or less 0  
Due after one year through five years 67,371  
Due after five years through ten years 540,472  
Due after ten years 0  
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis 607,843  
HTM securities, Amortized Cost 607,843  
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]    
Due in one year or less 0  
Due after one year through five years 66,888  
Due after five years through ten years 532,087  
Due after ten years 0  
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value 598,975  
HTM securities, Fair Value 598,975 0
U.S. agency bonds – mortgage-backed    
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]    
Amortized cost of securities without single maturities 1,471,782  
Amortized Cost 1,471,782 1,313,834
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair value of securities without single maturities 1,476,991  
Fair value 1,476,991 1,322,443
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount 0  
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]    
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value 0  
Asset-backed securities    
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]    
Amortized cost of securities without single maturities 165,719  
Amortized Cost 165,719 52,337
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair value of securities without single maturities 165,804  
Fair value 165,804 $ 54,780
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount 0  
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]    
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value $ 0