Annual report pursuant to Section 13 and 15(d)

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

v2.4.0.6
Available-for-Sale Securities, at Fair Value (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 13,666,954 $ 6,249,252
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 3,608,272 1,609,003
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 5,130,965 2,414,637
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value 2,272,866 1,029,517
Mortgage-backed Securities, Issued by Private Enterprises [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 2,654,851 $ 1,196,095