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, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, at fair value $ 9,171,511 $ 6,249,252
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 227,164 231,678
Available-for-sale Securities, Fixed Rate 7,000,442 4,821,479
Available-for-sale securities, at fair value 7,227,606 5,053,157
Mortgage-backed Securities, Issued by Private Enterprises [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 1,683,540 995,014
Available-for-sale Securities, Fixed Rate 260,365 201,081
Available-for-sale securities, at fair value 1,943,905 1,196,095
Collateralized Mortgage Backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale Securities, Adjustable Rate 1,910,704 1,226,692
Available-for-sale Securities, Fixed Rate 7,260,807 5,022,560
Available-for-sale securities, at fair value $ 9,171,511 $ 6,249,252