Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Available-for-Sale Securities, at Fair Value (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, at fair value $ 25,552,604 $ 21,220,819
Available-for-sale securities, at fair value, pledged as collateral for borrowings 25,200,000 21,000,000
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, at fair value 15,812,696 13,920,721
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, at fair value 4,930,963 3,616,967
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, at fair value 941,374 701,037
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale securities, at fair value $ 3,867,571 $ 2,982,094