Quarterly report pursuant to Section 13 or 15(d)

Available-for-sale Securities Classified by Rate Type (Details)

v2.4.0.6
Available-for-sale Securities Classified by Rate Type (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 14,963,531 $ 13,666,954
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 181,657 188,429
Available-for-sale Securities, Fixed Rate 11,750,898 10,823,674
Available-for-sale securities, at fair value 11,932,555 11,012,103
Mortgage-backed Securities, Issued by Private Enterprises [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 2,613,464 2,334,950
Available-for-sale Securities, Fixed Rate 417,512 319,901
Available-for-sale securities, at fair value 3,030,976 2,654,851
Collateralized Mortgage Backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 2,795,121 2,523,379
Available-for-sale Securities, Fixed Rate 12,168,410 11,143,575
Available-for-sale securities, at fair value $ 14,963,531 $ 13,666,954