Annual report pursuant to Section 13 and 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
Dec. 31, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Less than or equal to 1 year $ 230,893  
Greater than 1 year and less than or equal to 3 years 17,488,424  
Greater than 3 years and less than or equal to 5 years 1,812,870  
Greater than 5 years and less than or equal to 10 years 1,195,039  
Greater than 10 years 493,593  
Available-for-sale securities, at fair value 21,220,819 $ 13,116,171
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 14,242  
Greater than 1 year and less than or equal to 3 years 17,227,736  
Greater than 3 years and less than or equal to 5 years 826,816  
Greater than 5 years and less than or equal to 10 years 165,221  
Greater than 10 years 4,710  
Available-for-sale securities, at fair value 18,238,725 11,226,474
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Less than or equal to 1 year 216,651  
Greater than 1 year and less than or equal to 3 years 260,688  
Greater than 3 years and less than or equal to 5 years 986,054  
Greater than 5 years and less than or equal to 10 years 1,029,818  
Greater than 10 years 488,883  
Available-for-sale securities, at fair value $ 2,982,094 $ 1,889,697