Annual report pursuant to Section 13 and 15(d)

Available-for-Sale Securities, at Fair Value (Details)

v3.3.1.900
Available-for-Sale Securities, at Fair Value (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 7,825,320 $ 14,341,102
Available-for-sale Securities Pledged as Collateral 7,767,074 14,159,315
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 1,678,814 2,418,546
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 3,602,348 6,768,875
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 691,728 2,104,896
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 1,852,430 $ 3,048,785