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Resale and Repurchase Agreements (Remaining Contractual Maturities of Repurchase Agreements) (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Maturity Overnight [Member] | US Treasury and Government [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | $ 150,305 | $ 526,283
Maturity Overnight [Member] | US Government-sponsored Enterprise Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 32,575
Maturity Overnight [Member] | Agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 1,598,614 | 973,774
Maturity Overnight [Member] | Non-agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 62,742 | 71,399
Maturity Overnight [Member] | Asset-backed Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 155,917 | 60,012
Maturity Overnight [Member] | Other Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 33,668 | 50,375
Maturity Overnight [Member] | Repurchase Agreements [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 2,001,246 | 1,714,418
Maturity up to 90 days [Member] | US Treasury and Government [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity up to 90 days [Member] | US Government-sponsored Enterprise Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity up to 90 days [Member] | Agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 34,018 | 48,517
Maturity up to 90 days [Member] | Non-agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity up to 90 days [Member] | Asset-backed Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 40,000
Maturity up to 90 days [Member] | Other Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity up to 90 days [Member] | Repurchase Agreements [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 34,018 | 88,517
Maturity Greater than 90 Days [Member] | US Treasury and Government [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity Greater than 90 Days [Member] | US Government-sponsored Enterprise Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity Greater than 90 Days [Member] | Agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 220,849 | 227,802
Maturity Greater than 90 Days [Member] | Non-agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity Greater than 90 Days [Member] | Asset-backed Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity Greater than 90 Days [Member] | Other Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 0
Maturity Greater than 90 Days [Member] | Repurchase Agreements [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 220,849 | 227,802
Total Repurchase Agreements [Member] [Domain] | US Treasury and Government [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 150,305 | 526,283
Total Repurchase Agreements [Member] [Domain] | US Government-sponsored Enterprise Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 0 | 32,575
Total Repurchase Agreements [Member] [Domain] | Agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 1,853,481 | 1,250,093
Total Repurchase Agreements [Member] [Domain] | Non-agency mortgage-backed securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 62,742 | 71,399
Total Repurchase Agreements [Member] [Domain] | Asset-backed Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 155,917 | 100,012
Total Repurchase Agreements [Member] [Domain] | Other Debt Securities [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | 33,668 | 50,375
Total Repurchase Agreements [Member] [Domain] | Repurchase Agreements [Member] |  |
Schedule of Underlying Assets of Repurchase Agreements [Line Items] |  |
Assets Sold under Agreements to Repurchase, Repurchase Liability | $ 2,256,113 | $ 2,030,737

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- Definition [Line Items] for Schedule of Underlying Assets of Repurchase Agreements [Table] + References No definition available. + Details
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- Definition Amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 + Details
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