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
 3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Interest Rate 1.34% 1.31%
Assets Sold under Agreements to Repurchase, Weighted Average Maturity 94 days 77 days
Repurchase agreements $ 13,640,720 $ 9,316,351
US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Interest Rate 1.05% 0.94%
Repurchase agreements $ 11,484,929 $ 7,336,922
Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Interest Rate 2.77% 2.60%
Repurchase agreements $ 1,541,131 $ 1,434,145
Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Interest Rate 1.91% 1.69%
Repurchase agreements $ 86,571 $ 102,236
Commercial Real Estate Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Assets Sold under Agreements to Repurchase, Interest Rate 3.40% 3.16%
Repurchase agreements $ 528,089 $ 443,048
Maturity up to 30 days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 3,090,129 3,253,045
Maturity up to 30 days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 2,487,589 2,511,773
Maturity up to 30 days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 568,118 688,667
Maturity up to 30 days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 12,618 30,672
Maturity up to 30 days [Member] | Commercial Real Estate Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 21,804 21,933
Maturity 30 to 59 Days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 2,232,056 2,218,502
Maturity 30 to 59 Days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 1,897,082 1,786,664
Maturity 30 to 59 Days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 261,631 334,590
Maturity 30 to 59 Days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 45,862 68,257
Maturity 30 to 59 Days [Member] | Commercial Real Estate Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 27,481 28,991
Maturity 60 to 89 Days [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 2,993,260 1,128,394
Maturity 60 to 89 Days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 2,866,367 1,035,806
Maturity 60 to 89 Days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 126,893 89,281
Maturity 60 to 89 Days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 0 3,307
Maturity 60 to 89 Days [Member] | Commercial Real Estate Assets [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 2,029,157 1,444,056
Maturity 90 to 119 Days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 1,743,047 1,192,127
Maturity 90 to 119 Days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 272,694 251,929
Maturity 90 to 119 Days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 13,416 0
Maturity 90 to 119 Days [Member] | Commercial Real Estate Assets [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 3,080,853 1,086,720
Maturity 120 to 364 days [Member] | US Government Agencies Debt Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 2,490,844 810,552
Maturity 120 to 364 days [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 311,795 69,678
Maturity 120 to 364 days [Member] | Inverse Interest-Only Securities [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 14,675 0
Maturity 120 to 364 days [Member] | Commercial Real Estate Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 263,539 206,490
Maturity Over One Year [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements 215,265 185,634
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] | Commercial Real Estate Assets [Member]    
Assets Sold under Agreements to Repurchase [Line Items]    
Repurchase agreements $ 215,265 $ 185,634