Quarterly report pursuant to Section 13 or 15(d)

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

v3.2.0.727
Available-for-Sale Securities, at Fair Value (Details) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 12,807,658 $ 14,341,102
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 2,279,632 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 5,796,614 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 2,024,567 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 $ 2,706,845 $ 3,048,785