Quarterly report pursuant to Section 13 or 15(d)

Fair Value by Balance Sheet Grouping (Details)

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Fair Value by Balance Sheet Grouping (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Jun. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Available-for-sale securities, at fair value $ 20,199,094   $ 13,128,857      
Commercial real estate assets 2,171,344 $ 1,782,749 1,412,543 $ 1,114,548 $ 926,377 $ 660,953
Commercial real estate assets, at fair value 2,187,721   1,411,733      
Mortgage servicing rights, at fair value 930,613 $ 898,025 693,815 455,629 $ 427,813 493,688
Residential mortgage loans held-for-investment in securitization trusts, at fair value 3,031,191   3,271,317      
Residential mortgage loans held-for-sale, at fair value 31,197   40,146 723,174   811,431
Cash and cash equivalents 539,367   406,883      
Restricted cash 343,813   408,312 $ 264,872   $ 262,562
Derivative assets, at fair value 238,305   324,182      
Federal Home Loan Bank stock 85,175   167,856      
Equity investments 3,000   3,000      
Repurchase agreements 18,297,392   9,316,351      
Collateralized borrowings in securitization trusts, at fair value 2,785,413   3,037,196      
Federal Home Loan Bank advances 1,998,762   4,000,000      
Revolving credit facilities 40,000   70,000      
Convertible senior notes 282,543   0      
Convertible senior notes, at fair value 306,906   0      
Derivative liabilities, at fair value 11,312   12,501      
Federal Home Loan Bank of Des Moines [Member]            
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]            
Federal Home Loan Bank stock 85,176   167,856      
Federal Home Loan Bank advances $ 1,998,762   $ 4,000,000