Annual report pursuant to Section 13 and 15(d)

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

v3.3.1.900
Available-for-Sale Securities Classified by Rate Type (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
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 108,596 128,285
Available-for-sale Securities, Fixed Rate 5,864,294 11,164,032
Available-for-sale securities, at fair value 5,972,890 11,292,317
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 1,673,038 2,558,832
Available-for-sale Securities, Fixed Rate 179,392 489,953
Available-for-sale securities, at fair value 1,852,430 3,048,785
Collateralized Mortgage Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 1,781,634 2,687,117
Available-for-sale Securities, Fixed Rate 6,043,686 11,653,985
Available-for-sale securities, at fair value $ 7,825,320 $ 14,341,102