Quarterly report pursuant to Section 13 or 15(d)

Available-for-Sale Securities, Weighted Average Life Classifications (Details)

v3.8.0.1
Available-for-Sale Securities, Weighted Average Life Classifications (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]    
Less than or equal to 1 year $ 68,254  
Greater than 1 year and less than or equal to 3 years 143,236  
Greater than 3 years and less than or equal to 5 years 734,242  
Greater than 5 years and less than or equal to 10 years 15,956,664  
Greater than 10 years 4,156,981  
Available-for-sale securities, at fair value 21,059,377 $ 21,220,819
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Less than or equal to 1 year 9,912  
Greater than 1 year and less than or equal to 3 years 35,720  
Greater than 3 years and less than or equal to 5 years 289,226  
Greater than 5 years and less than or equal to 10 years 14,137,540  
Greater than 10 years 3,569,766  
Available-for-sale securities, at fair value 18,042,164 18,238,725
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Less than or equal to 1 year 58,342  
Greater than 1 year and less than or equal to 3 years 107,516  
Greater than 3 years and less than or equal to 5 years 445,016  
Greater than 5 years and less than or equal to 10 years 1,819,124  
Greater than 10 years 587,215  
Available-for-sale securities, at fair value $ 3,017,213 $ 2,982,094