Quarterly report pursuant to Section 13 or 15(d)

Schedule of Repurchase Agreements by Maturity (Details)

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Schedule of Repurchase Agreements by Maturity (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 23,806,631 $ 19,451,207
Weighted average borrowing rate 2.45% 1.69%
US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 21,504,889 $ 17,325,553
Weighted average borrowing rate 2.32% 1.53%
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 2,050,282 $ 1,941,911
Weighted average borrowing rate 3.59% 2.98%
Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 51,460 $ 71,243
Weighted average borrowing rate 3.20% 2.15%
Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 200,000 $ 112,500
Weighted average borrowing rate 4.37% 3.78%
Maturity up to 30 days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 6,910,626 $ 4,269,464
Maturity up to 30 days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 6,408,843 3,634,541
Maturity up to 30 days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 485,289 613,500
Maturity up to 30 days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 16,494 21,423
Maturity up to 30 days [Member] | Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity 30 to 59 Days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 2,465,288 3,831,111
Maturity 30 to 59 Days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 1,956,414 3,522,256
Maturity 30 to 59 Days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 494,990 261,835
Maturity 30 to 59 Days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 13,884 47,020
Maturity 30 to 59 Days [Member] | Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity 60 to 89 Days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 5,041 3,458,940
Maturity 60 to 89 Days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 5,041 3,165,834
Maturity 60 to 89 Days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 290,628
Maturity 60 to 89 Days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 2,478
Maturity 60 to 89 Days [Member] | Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity 90 to 119 Days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 5,535,994 2,452,426
Maturity 90 to 119 Days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 5,034,622 2,119,490
Maturity 90 to 119 Days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 501,372 332,614
Maturity 90 to 119 Days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 322
Maturity 90 to 119 Days [Member] | Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity 120 to 364 days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 8,689,682 5,326,766
Maturity 120 to 364 days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 8,099,969 4,883,432
Maturity 120 to 364 days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 568,631 443,334
Maturity 120 to 364 days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 21,082 0
Maturity 120 to 364 days [Member] | Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity Over One Year [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 200,000 112,500
Maturity Over One Year [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity Over One Year [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity Over One Year [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 0
Maturity Over One Year [Member] | Servicing Contracts [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 200,000 $ 112,500